OSAC 2022-S-0029 Standard Guide for Interpretation

and Reporting in Forensic Comparisons of Trace Materials

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OSAC 2022-S-0029 Standard 

Guide for Interpretation and 

Reporting in Forensic 

Comparisons of Trace 

Materials

Trace Materials Subcommittee

Chemistry: Trace Evidence Scientific Area Committee

Organization of Scientific Area Committees (OSAC) for Forensic Science
OSAC 2022-S-0029 Standard Guide for Interpretation

and Reporting in Forensic Comparisons of Trace Materials

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Draft OSAC Proposed Standard

OSAC 2022-S-0029

Standard Guide for Interpretation and 

Reporting in Forensic Comparisons of 

Trace Materials

Prepared by 

Trace Materials Subcommittee

Version: 1.0 - OSAC Open Comment

March 2022

Disclaimer:

This OSAC Proposed Standard was written by the Organization of Scientific Area Committees (OSAC) 

for Forensic Science following a process that includes an open comment period. This Proposed Standard 

will be submitted to a standards developing organization and is subject to change. 

There may be references in an OSAC Proposed Standard to other publications under development by 

OSAC. The information in the Proposed Standard, and underlying concepts and methodologies, may be 

used by the forensic-science community before the completion of such companion publications.

Any identification of commercial equipment, instruments, or materials in the Proposed Standard is not a 

recommendation or endorsement by the U.S. Government and does not imply that the equipment, 

instruments, or materials are necessarily the best available for the purpose.

To be placed on the OSAC Registry, certain types of standards first must be reviewed by a Scientific and 

Technical Review Panel (STRP). The STRP process is vital to OSAC’s mission of generating and 

recognizing scientifically sound standards for producing and interpreting forensic science results. The 

STRP shall provide critical and knowledgeable reviews of draft standards or of proposed revisions of 

standards previously published by standards developing organizations (SDOs) to ensure that the published 

methods that practitioners employ are scientifically valid, and the resulting claims are trustworthy.

The STRP panel will consist of an independent and diverse panel, including subject matter experts, human 

factors scientists, quality assurance personnel, and legal experts, which will be tasked with evaluating the 

proposed standard based on a comprehensive list of science-based criteria.
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For more information about this important process, please visit our website 

at: https://www.nist.gov/topics/organization-scientific-area-committees-forensic-science/scientifictechnical-review-panels.
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Standard Guide for Interpretation and Reporting in

Forensic Comparisons of Trace Materials

Designation

1 Scope

1.1 This guide covers recommendations for the overall interpretation and reporting of findings from an 

analytical scheme for trace material comparisons conducted by personnel in a forensic laboratory. 

1.2 This guide provides guidance to forensic examiners to standardize the interpretation of comparative 

examinations of trace evidence. It highlights fibers, glass, hair, paint, and tape but can be applied to 

other trace materials.

1.3 This guide describes the information that is included in trace evidence written reports regarding 

interpretation of the overall results of comparative examinations and includes example report 

wording. 

1.4 This standard is intended for use by competent forensic science practitioners with the requisite 

formal education, discipline-specific training (see Practices E2917, E3233, and E3234, WK56743), 

and demonstrated proficiency to perform forensic casework.

2 Referenced Documents

2.1 ASTM Standards:

E620 Practice for Reporting Opinions of Scientific or Technical Experts

E1610 Guide for Forensic Paint Analysis and Comparison

E1732 Terminology Relating to Forensic Science

E1967 Test Method for the Automated Determination of Refractive Index of Glass Samples Using the 

Oil Immersion Method and a Phase Contrast Microscope

E2224 Guide for Forensic Analysis of Fibers by Infrared Spectroscopy

E2225 Guide for Forensic Examination of Fabrics and Cordage

E2227 Guide for Forensic Examination of Non-Reactive Dyes in Textile Fibers by Thin-Layer 

Chromatography

E2228 Guide for Microscopical Examination of Textile Fibers

E2330 Test Method for Determination of Concentrations of Elements in Glass Samples Using 

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for Forensic Comparisons

E2808 Guide for Microspectrophotometry in Forensic Paint Analysis
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E2809 Guide for Using Scanning Electron Microscopy/X-Ray Spectrometry in Forensic Paint 

Examinations

E2917 Practice for Forensic Science Practitioners Training, Continuing Education, and Professional 

Development Programs

E2926 Test Method for Forensic Comparison of Glass Using Micro X-ray Fluorescence (μ-XRF) 

Spectrometry

E2927 Test Method for Determination of Trace Elements in Soda-Lime Glass Samples Using Laser 

Ablation Inductively Coupled Plasma Mass Spectrometry for Forensic Comparisons

E2937 Guide for Using Infrared Spectroscopy in Forensic Paint Examinations

E3085 Guide for Fourier Transform Infrared Spectroscopy in Forensic Tape Examinations

E3233 Practice for Forensic Tape Analysis Training Program

E3234 Practice for Forensic Paint Analysis Training Program

E3260 Guide for Forensic Examination and Comparison of Pressure Sensitive Tapes

WK56743 New Practice for Training in the Forensic Examination of Human Hair by Microscopy

WK72597 New Guide for the Microscopical Examination of Human Hair

WK72932 New Guide for Forensic Glass Analysis and Comparison

WK74138 Guide for Using Micro X-ray Fluorescence (-XRF) in Forensic Polymer Examinations

WK75180 Guide for Using Pyrolysis Gas Chromatography and Pyrolysis Gas Chromatography-Mass 

Spectrometry in Forensic Polymer Examinations

WK78747 Standard Guide for Forensic Examination of Fibers

WK78749 Standard Guide for Microspectrophotometry in Forensic Fiber Analysis

2.2 Other Documents

ISO/IEC 17025 General Requirements for the Competence of Testing and Calibration Laboratories

3 Terminology 

3.1 Definitions - For additional terms commonly employed for general forensic examinations see E1732.

3.2 Definitions of terms specific to this standard:

3.2.1 For definitions of terms used in this guide, refer to Terminology E1732. Additional definitions 

follow.
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Activity level: An aspect of comparative examination of evidence that considers factors such as transfer 

mechanisms and persistence.

Discussion. Factors include the presence of the evidence in a particular location (i.e., glass found 

embedded in the sole of a shoe versus glass found on a shirt), quantity (i.e., multiple fragments 

versus single fragment), and condition (i.e., pulled hair versus shed hair). 

Discussion. Alternative hypotheses of alleged activities may also be part of the factors considered.

Association: The opinion that there is more support for the proposition that two items originated from the 

same source as opposed to the proposition they originated from different sources.

Comparative report: A written report that includes an assessment of the significance of the comparative 

results from the analysis of two or more items to determine whether the items could have originated from 

the same or different sources. 

Cross-transfer: The two-way exchange of materials between objects that can occur when they come into 

contact with one another.

Relevant population: The pool of potential sources. 

Significance: The weight or meaning of the evidence or results.

Source level: An aspect of comparative examinations of evidence that considers whether the items 

originated from the same or different sources. 

Discussion. Consideration is given to how discriminating and rare the characteristics of the 

evidence are (i.e., glass fragments originated from antique glass versus the glass fragments 

originated from modern glass; the paint originated from a single layer of white paint versus the 

paint originated from a multi-layered, multi-colored paint).

Trace material: Physical evidence that can occur from the transfer of generally small quantities of 

materials (e.g., fibers, glass, hairs, paint, tape).
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4 Summary of Guide

4.1 This guide describes recommendations for the overall interpretation and reporting of findings from 

an analytical scheme for trace material comparisons, such as those involving fiber, glass, hair, paint, 

and tape.

4.2 This guide highlights the considerations associated with reaching an overall interpretation in trace 

material comparisons, including factors such as the properties of the items being analyzed, the 

analytical techniques applied in that analysis, and transfer and persistence considerations.

5 Significance and Use 

5.1 This guide uses a qualitative approach to communicate the significance of an association or 

exclusion, based on a) the validated methodology used for the comparison of the items, b) 

discrimination capabilities of the analytical protocol, and c) existing knowledge of how 

discriminating the compared characteristics are based on survey studies, reference collections, or 

databases. 

1. Note 3: The body of work supporting this guide is detailed in the 2020 trace evidence 

review article by Trejos, Koch, and Mehltretter [1].

5.2 This guide describes the use of an interpretation scale to assess relative significance of results in a 

comparison report of trace materials. 

6 Comparative Report Contents

6.1 The general requirements for reporting opinions of scientific or technical procedures should meet or 

exceed the requirements of Practice E620.

6.2 The following information is recorded: a listing of analytical techniques, results, interpretation, and 

opinions. The opinions include an interpretation of the significance of the results as well as a basis 

for the opined significance. The basis should include factors that limit or increase the significance of 

the opinion.

6.3 Examiners from the same discipline should be capable of reaching the same results based upon the 

report information and supporting analytical data within the case file.

6.3.1 Raw analytical data are retained in the case file for review.

6.3.1.1 Raw analytical data can be included in a comparative report only if a statement appears with an 

explanation and interpretation of their significance, to avoid misunderstanding of the data by the 

reader of the report.

7 Interpretation and Opinion Process 

7.1 In trace evidence comparisons, the examiner analyzes the evidence and resulting data, forms an 

opinion, and summarizes the findings in a written report. The examiner also interprets and reports 

the overall meaning of those findings. A three-step process can be used in forming the opinion. 

These steps can be conducted sequentially or simultaneously, depending on the methods used for the 

description and evaluation of the data. 
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7.1.1 Step one involves a binary decision to determine whether the compared samples can be 

discriminated based on the comparison of the data. 

7.1.2 Step two is the evaluation of the results on a source level to determine and explain the significance 

of finding differences or lack of differences between the samples being compared. 

7.1.3 Step three is the evaluation of these results on an activity level to determine and explain the 

relevance of the findings under given circumstances. 

7.2 This guide emphasizes the second step of interpretation at the source level and, when applicable, the 

third step of interpretation at the activity level. 

8 Significance Assessment

8.1 To reach an opinion, relevant data are acquired and evaluated using accepted scientific and logical 

principles and methodologies.

8.2 An assessment of the significance of the results is recorded in the report. 

8.2.1 When associations are made, they are communicated clearly and qualified properly in the report. 

Simple opinion statements (e.g., consistent with, could have come from, indistinguishable) are not 

sufficient on their own. 

8.2.2 An interpretation scale provides a framework for decision making for significance assessment and 

much of the rest of the document provides the framework for its application. 

8.2.3 Results should include the factors that support the reported significance.

8.2.4 For an assessment that uses data based on a relevant population, the examiner should disclose what 

population is considered relevant and if it is narrower than all possible sources. This information 

can be assessed through published discrimination studies, product manufacturing and distribution 

information, and databases.

8.2.5 In cases where there are multiple comparisons or cross-transfers, a separate opinion statement 

should be reached for each individual transfer. Cross-transfers or multiple transfers, when they 

occur, are examples of factors that could further increase the significance of findings. If so, an 

additional opinion statement regarding the significance of the combined individual transfers can be 

added.

8.3 The interpretation scale should be included in the report in its entirety to provide context for a 

specific interpretation. 

8.3.1 The following interpretation scale is an example for use in comparative examinations and uses a 

qualitative approach. However, when sufficient scientific data exist for a quantitative assessment 

of significance (e.g., error rates, frequencies of occurrence, likelihood ratios), such data can be used 

in conjunction with the qualitative assessment. The provenance of these data is provided either in 

the body of the report or included as an appendix to the report. When a database is used for this 

purpose, the use and limitations of the database are also included or made available upon request. 

8.3.2 Some interpretation categories are not applicable in every case or for every material type. This does 

not preclude a laboratory from establishing similar systematic criteria as that presented here. Refer 

to Sections 9 through 13 of this document for additional specific guidance.

Physical Fit – Physical Fit is the highest degree of association between items. It is the opinion 
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that the observations provide the strongest support for the proposition that the items were once 

joined together to form a single object as opposed to originating from different sources. Physical 

Fit is reached when the items that have been broken, torn, or separated exhibit physical features 

that correspond or re-align in a manner that is not expected to be replicated. A Physical Fit is 

not currently based upon a statistical evaluation of data; it is also not based upon exhaustive 

comparisons to all potential sources.

Associations of Evidence with Class Characteristics:

Class characteristics are physical, optical, or chemical properties that establish membership in a 

class, category, or group. Associations based on class characteristics do not establish that the 

items came from the same source. Class associations can have varying degrees of significance. 

In general, the smaller the size of the group relative to the relevant population, the more 

significant the association. These types of associations are categorized as follows:

Association with Highly Discriminating Characteristics – An association in which 

items could not be differentiated based on the examinations conducted. Therefore, the 

possibility that the items came from the same source cannot be eliminated. Additionally, 

the items share unusual characteristics that would rarely occur in the relevant population. 

This type of association provides very strong to extremely strong support for the 

proposition that the items originated from the same source as opposed to different 

sources. This is the highest degree of association that can be determined in the absence of 

a Physical Fit.

Association with Discriminating Characteristics – An association in which items could 

not be differentiated based on the examinations conducted. Therefore, the possibility that 

the items came from the same source cannot be eliminated. Other items have been 

manufactured or could occur in nature that would also be indistinguishable from the 

submitted items and could be encountered in the relevant population. This type of 

association provides moderately strong to strong support for the proposition that the items 

originated from the same source as opposed to different sources. The analytical 

techniques used in the analysis of these items can provide high levels of discrimination 

among natural and manufactured materials and therefore this is considered a strong

association.

Association with Limitations – An association in which items could not be 

differentiated based on the examinations conducted. Therefore, the possibility that the 

items came from the same source cannot be eliminated. This type of association provides 

slight to moderate support for the proposition that the items originated from the same 

source as opposed to different sources. As compared to the categories above, this type of 

association has decreased evidential value. The items are more commonly encountered in 

the relevant population, a complete analysis was not performed due to limited 

characteristics or a limited analytical scheme, or minor explainable variations were 

observed in the data. Minor variations could be due to factors such as having a sample of 

insufficient size to adequately assess heterogeneity of the entity from which it was 

derived.
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Inconclusive – No opinion could be reached regarding an association or an exclusion 

between the items.

Exclusion with Limitations – The item exhibits differences from the comparison sample that 

support that it did not originate from the source, as represented by the comparison sample; 

however, limiting factors prevented an Exclusion (Elimination) from being reached. This 

provides more support for the proposition that the items originated from different sources as 

opposed to the same source. 

Exclusion (Elimination) – The items exhibit differences that support an opinion that the two 

items did not originate from the same source.

9 Fiber Reporting

9.1 Fiber examination in forensic casework is typically a comparison of two or more fibers, usually from 

a questioned source and a known source, for the purpose of determining if the known source can be 

eliminated or included as a potential donor of the questioned fiber(s). Fiber analysis also involves the 

comparison of two or more questioned fibers to determine if they could share a common source.

9.2 Analytical methodologies used for fiber examination have a direct impact on significance 

assessments. 

9.2.1 A Physical Fit can only be reported when there is alignment of textile products along damaged, 

torn, or cut edges.

9.2.2 A comprehensive analytical scheme (see Guide WK78747) for natural and manufactured fibers, 

fabric and cordage (see Guide E2225) starts with a visual and microscopical examination to 

compare physical and optical characteristics such as color, shape, diameter, surface features, 

inclusions or delustrants, fluorescence, and birefringence (see Guide E2228). Additional techniques 

are used to further compare color or colorant [e.g., microspectrophotometry (MSP) (see Guide 

WK78749), thin layer chromatography (TLC) (see Guide E2227)]. In the case of manufactured 

fibers, instrumental techniques (e.g., FTIR, see Guide E2224) are used to examine and compare 

chemical composition.

9.2.2.1 A statement of decreased significance should be reported if a reduced analytical scheme was used 

to assess the physical, optical, and chemical characteristics that are routinely evaluated for 

samples of a given fiber type (e.g., limitations of the sample size or condition, absence of 

equipment routinely used).

9.2.3 Increased or decreased significance is based on available information for the relevant population

9.3 Source factors that could increase the significance of an association

9.3.1 Unusual physical or optical properties (e.g., variegated coloring, electrostatic core, fading, 

discoloration)

9.3.2 Corresponding surface contamination or damage

9.3.3 Unusual fiber type (e.g., aramid), depending on the scenario

9.3.4 Conditions that limit the possible sources of the fibers (e.g., fibers found embedded in a deployed 

airbag in a vehicle with a limited number of passengers wearing known garments)
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9.4 Source factors that could decrease the significance of an association

9.4.1 Limited number of relevant analytical techniques used in the comparison

9.4.2 Commonly observed fiber type, such as white cotton or blue denim cotton

9.4.3 Limited number of features available for comparison

9.4.4 Limited sample size

9.4.5 Condition of samples (e.g., degraded samples)

9.4.6 Minor physical or chemical differences between items being compared that could be a result of 

sample heterogeneity, contamination of the sample(s), or having a sample of insufficient size to 

adequately assess the homogeneity of the item from which it was derived

9.4.7 Circumstances where a narrow range of fiber type and color are likely to be encountered (e.g., 

same type of uniform worn by multiple people), which could lead to a random association

9.5 Example Scenarios for Each Interpretation Category

The following examples are provided to assist in reaching each interpretation category. 

9.5.1 Physical Fit

9.5.1.1 This interpretation category can be reached for fibers only when there is a physical fit of a textile 

piece with another textile along its torn, cut, or damaged edge, or through corresponding 

individual characteristics (e.g., surface features that carry across the pieces).

9.5.2 Association with Highly Discriminating Characteristics

9.5.2.1 Post-manufacturing mark on the items (e.g., both known and questioned items exhibit similar 

damage, staining, craft paint on surface)

9.5.2.2 Questioned to known association in which an unusual combination of characteristics, such as 

damage and color alteration, is present on both items

9.5.3 Association with Discriminating Characteristics

9.5.3.1 Questioned to known association in which a typical analysis scheme was performed (e.g., 

questioned nylon fiber corresponding to a known carpet)

9.5.4 Association with Limitations

9.5.4.1 Ubiquitous fibers (e.g., white cotton, blue denim cotton)

9.5.4.2 Limited characteristics to differentiate among fibers, depending on scenario (e.g., an undyed 

natural fiber or a colorless polyester fiber on a tape lift of a vehicle seat compared to a white 

cotton and polyester blend t-shirt)

9.5.4.3 Reduced analytical scheme due to lack of characteristics of the fiber or lack of available 

equipment

9.5.4.4 Limited amount of material for a comprehensive characterization or to adequately assess 

heterogeneity of the source from which it was derived

9.5.4.5 Minor explainable or demonstrable variation in one of the comparison samples due to established 

causes such as damage (e.g., impact), alteration (e.g., heat or chemical exposure), or known 

contamination (e.g., biological fluids) 
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9.5.5 Inconclusive

9.5.5.1 The questioned fiber possesses similar characteristics to the known sample but also exhibits some 

differences. These differences could be attributed to a time differential between the date of the 

incident and the collection date of the known sample, post-depositional changes, the known

sample not being truly representative, or because the questioned fiber is from a different source.

9.5.5.2 The questioned or known fibers are too damaged, degraded, or contaminated to conduct most 

examinations.

9.5.6 Exclusion with Limitations

9.5.6.1 The questioned fiber is dissimilar in physical properties or chemical composition in comparison 

to the known, suggesting the items did not originate from the same source; however, these 

dissimilarities are insufficient for a definitive exclusion due to limiting factors. Limiting factors 

include indications of change or damage that could be from exposure to heat, chemicals, or 

environmental effects; or limited amount of known sample of a suspected source that is highly 

variable (e.g., trunk liner). 

9.5.7 Exclusion (Elimination)

9.5.7.1 Exclusionary differences in physical, optical, or chemical properties between the compared fibers

9.6 Example Wording for Interpretation Categories

9.6.1 Physical Fit

9.6.1.1 “The torn edge of the questioned fabric piece physically fits and aligns with the torn edges of the

known shirt fabric. This provides extremely strong support for the proposition that the fabric 

piece originated from and was at one time part of the shirt, as opposed to the proposition it 

originated from and was a part of another torn fabric source (Physical Fit).”

9.6.1.2 "The cut end of the questioned cordage piece physically fits and aligns with the cut end of the 

known cordage. This provides extremely strong support for the proposition that the cordage piece 

originated from and was at one time part of the known cordage, as opposed to the proposition it 

originated from and was a part of another cut cordage source (Physical Fit).”

9.6.2 Association with Highly Discriminating Characteristics

9.6.2.1 “Questioned fibers were compared to the sample of fibers from the known textile using (insert 

methods here). A singed, purple polyester questioned fiber corresponds in (insert characteristics 

here) to the singed fibers that comprise the sample of known purple textile. Therefore, the 

questioned fibers either originated from the known textile or from another textile with the same 

manufactured and acquired characteristics (Association with Highly Discriminating 

Characteristics). This type of association was reached because no differences were observed 

between the fibers and because of the similar damage to both items.”

9.6.2.2 “Questioned fibers were compared to the fibers sampled from the known textile using (insert 

methods here). The multi-colored questioned fibers correspond in (insert characteristics here) 

along their length to the multi-colored fibers that comprise the sample from the known textile. 

Therefore, the questioned fibers either originated from the known textile or from another textile 

with the same manufactured characteristics (Association with Highly Discriminating 

Characteristics). This type of association was reached because no differences were observed 

between the fibers and because of the number and arrangement of colors in both items.”
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9.6.2.3 “Questioned cordage was compared to the sample of the known cordage using (insert methods 

here). The questioned cordage corresponds in (insert characteristics here) to the sample of 

known cordage, and both items contain extensive fraying. Therefore, the questioned cordage 

either originated from the known cordage or from another source of cordage with the same 

manufactured and acquired characteristics (Association with Highly Discriminating 

Characteristics). This type of association was reached because no differences were observed 

between the cordage and because of the damage observed on both items.”

9.6.3 Association with Discriminating Characteristics

9.6.3.1 “Questioned fibers were compared to the sample of fibers comprising the known textile using 

(insert methods here). Brown nylon fibers correspond in (insert characteristics here) to the 

sample of brown nylon fibers that comprise the known textile. Therefore, the questioned fibers 

either originated from the known textile or from another textile with the same characteristics 

(Association with Discriminating Characteristics). This type of association was reached 

because other textiles containing fibers made to the same specifications (type, color, microscopic 

characteristics, etc.) would also be indistinguishable from these fibers. The techniques utilized in 

this comparative analysis can readily distinguish different fibers.”

9.6.3.2 "Questioned cordage was compared to the sample of known cordage using (insert methods here). 

Brown nylon yarns that comprise the questioned cordage correspond in (insert characteristics 

here) to the sample of brown nylon yarns that comprise the known cordage. Therefore, the 

questioned cordage either originated from the known cordage or from another source of cordage 

with the same characteristics (Association with Discriminating Characteristics). This type of 

association was reached because other cordage containing yarns made to the same specifications 

(type, color, microscopic characteristics, etc.) would also be indistinguishable from these yarns. 

The techniques utilized in this comparative analysis can readily distinguish different yarns."

9.6.4 Association with Limitations

9.6.4.1 “Questioned fibers were compared to fibers comprising the sample from the known textile using 

(insert methods here). Round, colorless polyester fibers correspond in (insert characteristics 

here) to the round, colorless polyester fibers that comprise the sample from the known textile. 

Therefore, the questioned fibers either originated from the known textile or from another textile 

with the same characteristics (Association with Limitations). This type of association was 

reached because of the limited number of distinguishing characteristics available for comparison 

between the known and the questioned fibers as well as the prevalence of this fiber type.”

9.6.4.2 “Questioned fibers collected from the dashboard of the vehicle were compared to fibers 

comprising the sample from the known textile using (insert methods here). The impacted red 

nylon fibers from the dashboard correspond in (insert characteristics here) to the red nylon fibers 

that comprise the sample from the known textile. However, slight differences were noted in 

(insert characteristics here) of the questioned fibers in comparison to the fibers from the sample 

of the known textile. These slight differences are explainable due to observed damage. Therefore, 

the questioned fibers either originated from the known textile or from another textile with the 

same characteristics (Association with Limitations). This type of association was reached 

because of the minor variations observed in the characteristics between the known and the 

questioned fibers."

9.6.5 Inconclusive
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9.6.5.1 “Questioned fibers were compared to fibers comprising the sample collected from the known 

textile using (insert methods here). The red nylon fibers correspond in (insert characteristics 

here) to the red nylon fibers that comprise the known textile. However, slight differences were 

noted in the (insert characteristics here) of the questioned fibers in comparison to the sample of 

the known textile. Because of the documented potential exposure of the questioned fibers to the 

environment (based on case information communicated by the submitting agency), no opinion 

can be reached as to whether the red fibers originated from the textile or from another source of 

red fibers (Inconclusive).”

9.6.6 Exclusion with Limitations

9.6.6.1 “Questioned fibers were compared to fibers composing the samples from the known trunk liner 

using (insert methods here). The questioned fibers were different in (insert characteristics here) 

to the fiber samples from the known trunk liner, indicating the items did not originate from the 

same source; however, possible reasons for this difference include that the source is highly 

variable, and the questioned and known fiber samples provided are not fully representative of 

their source. Therefore, this difference is insufficient for a definitive exclusion (Exclusion with 

Limitations).” 

9.6.6.2 “Questioned cordage was compared to the sample of known cordage using (insert methods here). 

The outer braided layer of the cordage is similar, but the core was different in (insert 

characteristics here), indicating the items did not originate from the same source; however, 

possible reasons for the difference include manufacturing variation or irregularities. Therefore, 

this difference is insufficient for a definitive exclusion (Exclusion with Limitations).”

9.6.7 Exclusion (Elimination)

9.6.7.1 “Questioned fibers were compared to the fibers comprising the known textile using (insert 

methods here). The fibers are different in (insert characteristics here) from the fibers comprising 

the textile. Therefore, the questioned fibers did not originate from the textile [Exclusion 

(Elimination)].”

9.6.7.2 "Questioned yarns were compared to the sample of known cordage using (insert methods here). 

The questioned yarns are different in construction from the yarns that comprise the reference 

sample of cordage. Therefore, the questioned yarns did not originate from the known cordage 

[Exclusion (Elimination)]."

9.7 Activity Level Considerations

9.7.1 Activity factors that could increase the overall significance of the association(s)

9.7.1.1 Large number of fibers or a portion of a textile transferred

9.7.1.2 Location where the fibers are found (e.g., under fingernail, in damaged area of vehicle)

1. Note 1: Be aware that fibers can move within packaging or during transport of evidence.

9.7.1.3 Cross-transfer of fibers between two sources

9.7.1.4 Fiber fusions (e.g., fiber embedded in or on a vehicle during an impact)

9.7.1.5 While certain fiber types are considered ubiquitous because they are commonly found in the 

environment (e.g., white cotton, blue denim cotton), activity factors should be considered to 

determine if the fibers are relevant and add significance.
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9.7.2 Activity factors that could decrease the overall significance of the association(s)

9.7.2.1 Reasonable explanation as to why there was a transfer of fiber(s) (e.g., two individuals known to 

be in close or frequent contact)

9.7.3 Transfer and persistence

9.7.3.1 Transfer and persistence factors are considered when evaluating questions about alleged activities 

and the presence of fibers.

9.7.3.2 Textile fibers are transferred either by direct (primary) or indirect (secondary, tertiary) transfer. 

The possibility of transfer depends on the types of fabric or surface involved in the contact and 

the nature and duration of the contact. 

9.7.3.3 The number of questioned fibers associated with a known source is important in estimating actual 

contact. The greater the number of fibers, the more likely that direct and potentially recent contact 

occurred between fiber sources. The converse is not necessarily true, however, and even one fiber 

association can have probative value. Additionally, finding no fibers does not necessarily mean 

that no contact occurred. Each case is different, and all of the relevant factors should be 

considered before determining the significance of the evidence.

9.7.3.4 The type of physical contact between two sources influences the number of fibers transferred and 

the value placed on their discovery. Physical contact of an extended duration or of a forceful 

nature can result in many fiber transfers. Brief contact is less likely to result in the transfer of 

multiple fibers.

9.7.3.5 Fabric construction affects the number and types of fibers that could transfer. For example, tightly 

woven or knitted fabrics shed fewer fibers than loosely knit or woven fabrics. Fabrics composed 

of filament fibers shed less than fabrics composed of staple fibers.

9.7.3.6 The condition and wear of the fabric also affects the degree of fiber transfers. Newer fabrics can 

have an abundance of loosely adhering fibers on the surface of the fabric. Well-worn fabrics 

typically do not have loosely adhering surface fibers but can have damaged areas that easily shed 

fibers. Damage to a fabric caused during physical contact increases the possibility of fiber 

transfer.

9.7.3.7 Transferred fibers are typically lost at an exponential rate. The rate of loss can vary depending on 

the types of fabrics involved, the activity of the individual or item (or lack thereof), and the 

environmental conditions (e.g., wind, rain) to which the evidence was exposed after contact. 

While it is impossible to precisely predict how many transferred fibers will remain after a given 

period of time, it is important for investigators to retrieve and protect evidence as soon as 

possible.

9.7.3.8 Background information regarding the sources involved (e.g., textiles, individuals) and possible

prior contact between them can affect the significance of the association.

9.7.4 Cross-transfers or multiple transfers of fibers. If many different fibers are associated between 

known and questioned sources (e.g., two or more articles of clothing had fibers transfer from them, 

one shirt had two different fiber types transfer to it, fibers from multiple sources in a location 

transferred to a victim), then the possibility that contact occurred between these items could be 

increased. Multiple transfers or cross-transfers reduce the chance that the fibers were all deposited 

by coincidence.
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9.7.4.1 When two or more associations are being reported, each association should be reported 

separately. Additional text can then be included describing whether and how the multiple reported 

associations could affect the overall significance assessment and opinions from the totality of the 

examination results.

9.7.5 Example Wording for Activity Level Considerations 

9.7.5.1 “The large number of fibers recovered from Item 1 indicates direct contact occurred with a 

textile.”

9.7.5.2 “The fibers embedded in the damaged area of the suspect vehicle indicates that the vehicle has 

been in forceful contact with a fabric-clad item.”

9.7.5.3 Ubiquitous fibers. “Although the fibers were blue denim cotton, which are commonly found in 

the environment, finding blue denim cotton fibers embedded in the damaged area of the vehicle 

lends more significance to their evidentiary value.”

9.7.5.4 Cross-transfer. “The presence of numerous fibers on the victim’s shirt that could not be 

distinguished from the fibers comprising the known shirt from the subject and the presence of 

numerous fibers on the subject’s shirt that could not be distinguished from the fibers comprising 

the known shirt from the victim provides stronger support for contact having occurred between 

the two shirts than either transfer alone. Cross-transfers reduce the chance that the fibers were all 

deposited by coincidence.”

9.7.5.5 Multiple transfers. “The presence of fibers on the victim's shirt that could not be distinguished 

from the fibers comprising both the known shirt and the known pants from the subject provides 

stronger support for contact having occurred from the subject's shirt and pants to the victim’s shirt 

than either transfer alone. Multiple transfers reduce the chance that the fibers were all deposited 

by coincidence.”

10 Glass Reporting

10.1 Glass examination in forensic casework is typically a comparison of two or more glass fragments to 

determine if they can be discriminated by their physical, optical, or elemental composition. If the 

samples are distinguishable in one or more of these observed and measured properties, it is reported 

that they do not originate from the same broken glass object represented by the submitted known 

sample. If the samples are indistinguishable in all of these observed and measured properties, the 

possibility that they originated from the same broken glass object cannot be eliminated.

2. Note 2: It is important to note, however, that although there could be several objects with 

identical properties, glass fragments can originate only from broken and not intact objects.

10.2 Analytical methodologies used for glass comparisons have a direct impact on significance 

assessments. 

10.2.1 A Physical Fit can only be reported when there is alignment of two glass fragments along their 

broken edges.

10.2.2 A comprehensive analytical scheme (see Guide WK72932), unless sample size or condition 

prohibits it, includes visual and microscopical examinations and characterization of the glass by its 

optical properties (see Test Method E1967) and elemental composition.

10.2.3 Increased or decreased significance is stated based on the techniques used for the examination and 
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respective discrimination capabilities and on frequency of occurrence or random match 

probabilities from glass populations.

10.2.3.1 Analytical sensitivity and precision of the methods used for elemental analysis, along with the 

observed variations within and between samples in the relevant population, allow for high 

discrimination between different sources. The use of Inductively Coupled Plasma-Mass 

Spectrometry (ICP-MS) (see Test Method E2330), micro-X-Ray Fluorescence Spectroscopy 

(μXRF) (see Test Method E2926), or Laser Ablation-ICP-MS (LA-ICP-MS) (see Test Method 

E2927) is recommended for elemental analysis and comparison of glass when sufficient sample is 

available.

10.2.3.2 Due to the ability of the sensitive elemental techniques in 10.2.3.1 to differentiate glass 

manufactured in different plants, use of one of these techniques is required to report a potential 

association of increased significance. Since there are many manufacturing plants producing glass 

over many years, coincidental indistinguishable elemental composition can exist but are not 

frequent. Random match rates around 0.1% have been observed in different sample sets [2-4].

10.2.3.3 In reporting a potential association, a statement of decreased significance is reported if the 

analytical scheme does not include elemental analysis at all or if the elemental analysis is 

conducted by less sensitive methods such as scanning electron microscopy – energy dispersive xray spectroscopy (SEM-EDS). 

1. Note 3 - The sensitivity of SEM-EDS is not suitable to detect those trace elements known 

to differentiate glass fragments, but SEM-EDS can detect differences between glasses based on 

major and, in some instances, minor elemental concentrations. 

2. Note 4 - SEM-EDS analysis of glass can be conducted to characterize sources (i.e., float 

vs. container vs. leaded glass) or for comparative analysis when the small size of the sample 

prevents the analysis by more discriminating methods.

10.2.4 Glass examinations generate quantitative data (RI and elemental composition) that allow the 

application of statistical methods to make decisions about differences or similarities between 

samples. The laboratory or examiner selects a criterion that is appropriate to the analytical method 

used to generate the data and that has acceptable/known error rates.

10.2.4.1 Access to and use of databases is recommended to evaluate the rarity of measured features or to 

estimate a frequency of random match or a likelihood ratio (LR) to provide an objective measure 

of significance. Databases developed and validated in forensic laboratories or reported in the 

peer-reviewed literature can be used to estimate a quantitative measure of the significance 

through frequency of random match or LR estimations to describe the value of the glass evidence.

10.3 Source factors that could increase the significance of an association

10.3.1 Unusual physical features, such as unusual weathering markings, labeling (or partial labeling) of 

Department of Transportation (DOT) numbers, or manufacturer markings (e.g., headlamp)

10.3.2 Glass with a known limited population or rare characteristics (e.g., glass with unusual RI, custom 

made glass, glass with coatings, ultra-clear low Fe glass, sheet glass with unusually high 

concentrations of elements such as Er, Mo, Ce, Se)

10.3.3 Thermal history of the sample (if the compared glass fragments were both exposed to the same 

environmental temperature conditions, e.g., fire or explosion)
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10.4 Source factors that could decrease the significance of an association

10.4.1 Analytical scheme does not include an assessment of both the optical and trace elemental 

composition of the glass

10.4.2 Condition of samples (e.g., small sample size)

10.4.3 Thermal history of the sample (if the compared glass fragments were exposed to different 

environmental temperature conditions, e.g., fire) 

3. Note 5 - Exposure to heat (e.g., fire) could affect the optical properties prior to annealing but 

not the elemental profile.

10.4.4 Properties that are not very discriminating, such as a relatively common RI

10.5 Example Scenarios for Each Interpretation Category

The following examples are provided to assist in reaching each interpretation category.

10.5.1 Physical Fit

10.5.1.1 This interpretation category can be reached for glasses only when there is a physical fit (fracture 

fit) of two or more pieces of broken glass or through corresponding individual characteristics 

(e.g., surface features such as number, letter or a patterned label) that carry across the pieces.

10.5.2 Association with Highly Discriminating Characteristics

10.5.2.1 Association of glass fragments characterized by elemental analysis using ICP-based methods 

alone, or ICP-based methods in combination with physical or optical measurements (RI)

10.5.2.2 Association of glass fragments characterized by RI and elemental analysis using μXRF when 

elements with atomic number equal to or greater than 37 (Rb) are present above the limit of 

quantitation

10.5.2.3 Association of glass fragments for which the estimated random match probability of the measured 

properties is very small (e.g., smaller than 0.2%) [2-5]

10.5.2.4 Association of glass fragments for which the estimated calibrated likelihood ratios (LR) provide 

very strong to extremely strong support for the same-source hypothesis over the different-source 

hypothesis (e.g., LR greater than 1000) [1, 4]. Note that the example given (LR greater than 

1000) is not meant as a strict cutoff to determine whether a calibrated LR provides very strong to 

extremely strong support for the same-source hypothesis. The calibrated LR, as well as the upper 

and lower limits of possible calibrated LRs, will depend on the background database and 

calibration procedure used for the LR calculations. 

10.5.3 Association with Discriminating Characteristics

10.5.3.1 Association of glass fragments characterized by elemental analysis using μXRF alone, when 

elements with atomic number equal to or greater than 37 (Rb) are present above the limit of 

quantitation

10.5.3.2 Association of glass fragments characterized by elemental analysis using RI and μXRF, when 

elements with atomic number equal to or greater than 37 (Rb) are below the limit of quantitation

10.5.3.3 Association of glass fragments for which the estimated random match probability of the measured 

properties is small (e.g., between 0.2% and 2%) [1-5]
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10.5.3.4 Association of glass fragments for which the estimated calibrated likelihood ratios provide 

moderately strong to strong support for the same-source hypothesis over the different-source 

hypothesis (e.g., LR between 100 and 1000) [4]. Note that the example given (LR between 100 

and 1000) is not meant as a strict limited range to determine whether a calibrated LR provides 

moderately strong to strong support for the same-source hypothesis. 

10.5.4 Association with Limitations

10.5.4.1 Reduced analytical schemes (e.g., only RI or RI and elemental analysis by SEM-EDS)

10.5.4.2 Limited sample or sample condition that prevents adequate characterization

10.5.4.3 Association of glass fragments for which the estimated random match probability of the measured 

properties is relatively high (e.g., greater than 2%) [2-5]

10.5.4.4 Association of glass fragments for which the estimated calibrated likelihood ratios provide weak 

to moderate support for the same-source hypothesis over the different-source hypothesis (e.g., LR 

between 1 and 100) [1, 4]. Note that the example given (LR between 1 and 100) is not meant as a 

strict limited range to determine whether a calibrated LR provides weak to moderate support for 

the same-source hypothesis. 

10.5.5 Inconclusive

10.5.5.1 The questioned glass is insufficient to do most examinations (e.g., physical/optical examinations 

can identify the sample as glass, but the sample is too small for other comparison methods).

10.5.6 Exclusion with Limitations (not applicable)

10.5.7 Exclusion (Elimination)

10.5.7.1 Physical, chemical, or optical exclusionary differences between the compared glasses

10.6 Example Wording for Interpretation Categories

10.6.1 Physical Fit

10.6.1.1 “A physical/fracture fit was identified/observed based on corresponding random characteristics 

on the broken edges of the Item 1 piece of glass and the broken edges of Item 2, the known

source. Therefore, this correspondence provides extremely strong support for the proposition that 

they were once part of the same broken glass object and extremely weak support for the 

proposition that the glass came from different broken glass objects (Physical Fit).”

10.6.2 Association with Highly Discriminating Characteristics

10.6.2.1 “The Item 1 known glass fragments and the Item 2 questioned glass fragment are colorless glass 

(specify color when possible) that show characteristics of tempered glass (specify glass type when 

possible, e.g., flat, float, container glass). Comparison of Items 1 and 2 by visual and 

microscopical techniques, refractive index, and elemental analysis by LA-ICP-MS (specify 

sensitive technique here) determined that they could not be differentiated based on their physical 

and optical characteristics or their elemental composition. These combined methods have shown 

to be highly discriminating between glass sources. Therefore, the questioned glass originated 

from the window (specify the known source, e.g., sheet of glass, window, windshield) as 

represented by the known sample or another source of broken glass indistinguishable in the 

measured properties (Association with Highly Discriminating Characteristics). This type of 

association was reached because coincidental associations of glass originating from different 
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sources could occur but are expected to be highly unusual.”

10.6.3 Association with Discriminating Characteristics

10.6.3.1 “All glass fragments received as Item 1 (known) and the glass fragment received as Item 2 

(questioned) are colorless glass (specify color when possible) that show characteristics of flat 

glass (specify glass type when possible e.g., tempered, flat, float, container glass, etc.). 

Comparison of Items 1 and 2 by visual and microscopical techniques, refractive index and 

elemental composition by μXRF (specify sensitive technique here) determined that they could not 

be differentiated based on their physical and optical characteristics and their elemental 

composition. These combined methods have shown to be discriminating between glass sources. 

Therefore, the questioned glass originated from the windshield (specify the known source, e.g., 

sheet of glass, window, windshield) submitted as a known sample or another source of broken 

glass indistinguishable in the measured properties (Association with Discriminating 

Characteristics). This type of association was reached because coincidental associations of glass 

originating from different sources could occur but are expected to be unusual.”

10.6.4 Association with Limitations

10.6.4.1 “The glass fragment received as Item 1 (questioned glass) and the glass fragments received as 

Item 2 (known) are indistinguishable in their refractive indices. Therefore, the questioned glass 

originated from the known window or another source of glass with the same refractive index. 

(Association with Limitations). This type of association was reached due to the limited number 

of characteristics available for comparison between the known and questioned sample. In glass 

specimens where only refractive index data can be measured, the chance of finding coincidental 

associations is significantly greater. More discriminating techniques could not be applied due to 

the limited size of the questioned sample.”

10.6.4.2 “The glass fragment received as Item 1 (questioned glass) and the glass fragments received as 

Item 2 (known) are indistinguishable by refractive index and elemental analysis with SEM-EDS. 

Therefore, the questioned glass originated from the known window or another source of glass 

with the same refractive index and elemental composition (Association with Limitations). This 

type of association was reached due to the limited number of characteristics available for 

comparison between the known and questioned sample. In glass specimens where only refractive 

index and SEM-EDS data can be measured, the chance of finding coincidental associations is 

significantly greater. SEM-EDS is limited to the detection of major and minor elements but not 

suitable for detection of trace elements. More discriminating techniques could not be applied due 

to the limited size of the questioned sample.”

10.6.5 Inconclusive

10.6.5.1 “Although there are some similarities between the Item 1 questioned glass and the Item 2 

container, the fragment size of Item 1 does not allow for the complete comparison of optical or 

chemical properties. Therefore, no opinion can be reached regarding an association or exclusion 

between items (Inconclusive).”

10.6.5.2 “Although there are some similarities between Item 1 and Item 2, the quantity of glass fragments 

received as the Item 2 known sample is insufficient to completely characterize the optical and 

elemental composition of the known broken source. Therefore, no opinion can be reached 

regarding an association or exclusion between items (Inconclusive).”

10.6.6 Exclusion with Limitations (not applicable)
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10.6.7 Exclusion (Elimination)

10.6.7.1 “The Item 1 glass fragment differs in physical and optical properties from the Item 2 windshield, 

and therefore the known glass source represented as Item 2 is not the source of Item 1 [Exclusion 

(Elimination)].

10.6.7.2 “The Item 1 glass fragment differs in physical, optical, and chemical properties from the Item 2 

bottle, and therefore Item 2 is not the source of Item 1 [Exclusion (Elimination)].”

10.6.7.3 “The Item 1 glass fragment differs in elemental composition from the Item 2 window, and 

therefore Item 2 is not the source of Item 1 [Exclusion (Elimination)].”

10.7 Activity Level considerations

10.7.1 Activity factors that could increase the overall significance of the association(s)

10.7.1.1 Large number of fragments transferred from a single source

10.7.1.2 Large number and size of fragments transferred and retained on the recipient

10.7.1.3 Location where the glass is found (e.g., upper surface of the shoe versus embedded in the sole of 

the shoe)

10.7.2 Activity factors that could decrease the overall significance of the association(s)

10.7.2.1 Location where the glass is found (e.g., embedded in the sole of the shoe versus on the upper 

surface of the shoe)

10.7.2.2 Inability to determine the location of fragments on a searched surface (e.g., fragments recovered 

in the evidence container or garment improperly wrapped)

10.7.3 Transfer and persistence

10.7.3.1 Transfer and persistence factors are considered when evaluating questions about alleged activities 

and the presence of glass.

10.7.3.2 The breaking of glass generates small fragments that can be transferred to a person or to other 

objects in the vicinity of the breaking glass. Transfer and persistence factors are considered in 

evaluation of the significance of the findings within a specific set of circumstances.

10.7.3.3 The understanding of the phenomena of transfer and persistence of glass fragments is 

fundamental for the interpretation and assessment of the significance of the evidence. 

10.7.3.4 The number and size of fragments transferred and retained on the recipient is related to several 

factors such as type of clothes and garments, distance from the breaking window, wet versus dry 

clothing, type and thickness of glass, the breaking force, the number of blows, and the object that 

broke the glass item. 

10.7.4 The value of evidence can be enhanced by the cross-transfer of evidence between victim and 

suspect, cross-transfer between objects, or the transfer of multiple items of evidence. 

10.7.4.1 In instances in which two or more associations are being reported, each association should be 

reported separately. Additional text can be included describing whether and how the multiple 

reported associations can affect the overall significance assessment and opinions from the totality 

of the examination results.

10.7.5 Example Wording for Activity Level Considerations 
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10.7.5.1 “The large number of glass fragments recovered from item 1 indicates a recent exposure to 

broken glass.”

10.7.5.2 “It is rare to find broken glass fragments in the head hair of persons not involved in glassbreaking activities.”

11 Hair Reporting

11.1 Hair examination in forensic casework can consist of the microscopical comparison of questioned 

hairs to hairs from a known source to determine if the known source can be eliminated or included as 

a potential donor of the questioned hair 

11.1.1 Hair comparisons typically consist of determining if a questioned hair is consistent in macroscopic 

and microscopic characteristics to the hairs submitted as a known sample. 

11.2 A comprehensive analytical scheme (see Guide WK72597) includes visual and microscopical 

examination and comparison using a comparison microscope to assess and compare characteristics.

11.2.1 The presence, absence, and distribution of the macroscopic and microscopic characteristics present 

in a hair have a direct impact on its significance. 

11.2.1.1 Hair from a single source is not homogeneous in microscopic characteristics and has a range of 

characteristics that could be present. These characteristics change over time. 

11.2.1.2 A person can have hairs that have different macroscopic or microscopic characteristics from the 

majority of the hairs from the same somatic area. 

11.2.1.3 If the macroscopic and microscopic characteristics of a questioned hair falls within the range of 

the characteristics of the hairs in known source, the known source can be included as a potential 

donor of the questioned hair. When the known source is included as a potential donor, the 

following statement or an equivalent statement is included in the report: “Microscopical hair 

comparisons are not a means of personal identification. The number of individuals that could be 

included as a possible source is unknown.”

11.2.2 The result of a hair comparison could be affected if a known hair sample is very limited (e.g., 

contains one known hair), if the question hair is a fragment (i.e., cut or broken), if the questioned 

and known samples lack pigment, or if a significant amount of time has elapsed between the 

incident and known sample collection. Additional qualifying statements can be added to the report 

in situations where there are known circumstances that affect the examination.

11.2.3 The range of macroscopic and microscopic characteristics within the hairs from a single source 

could overlap with the range of characteristics of hairs from another source. Due to this overlap, it 

is possible that a questioned hair cannot be differentiated from multiple sources. In this case, a 

statement is added to the report that both sources of the known hair samples (persons A and B) can 

be included as possible sources of the questioned hair.

11.2.4 As a part of a microscopical comparison, hairs may be classified by ancestry. If ancestry 

classifications are reported, the following statement or an equivalent statement is included: 

“Ancestral classifications of hairs are based on the combination of macroscopic and microscopic 

characteristics which are typically observed in hairs from individuals of a given ancestral group, 

and these classifications may or may not correspond to an individual’s ancestry origin or selfidentification.” 
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11.2.5 As a part of a microscopical comparison, hairs may be classified by body area. If body area 

classifications are reported, the following statement or an equivalent statement is included: “Body 

area classifications of hairs are based on the combination of macroscopic and microscopic 

characteristics which are typically observed in hairs from specific areas of the body.” 

11.2.6 DNA testing is considered after microscopical comparisons. When probative results are 

determined by a microscopical analysis of hairs, subsequent DNA analysis could provide additional 

information. Statements recommending subsequent DNA testing are included in the report, such 

as: “These results should be evaluated in conjunction with DNA analysis.” Further discussion of 

DNA analysis of hairs is beyond the scope of this document. 

11.2.7 Results presented in written reports cannot include statistical or numerical estimates of rarity or 

error rate because generally accepted estimates of these quantities have not yet been reliably 

established. This prohibition includes unfounded statistical statements (e.g., opinions based on 

years of experience, number of hairs or hair samples examined by examiner, or the number of 

examinations performed by the examiner) regarding a forensic hair examiner’s potential error rate 

or the numerical likelihood that a questioned hair came from a specific individual.

11.3 Source factors that could increase the significance of an association

11.3.1 Dyed hair where both the natural color and the dyed color are present

11.3.2 Hair that has been dyed with different, distinctive colors multiple times

11.3.3 Disease, hereditary hair conditions, or unusual characteristics (e.g., head hairs with pilli annulati, a 

double medulla, hairs exhibiting characteristics from external causes)

11.3.4 Conditions that limit the possible sources of the hair (e.g, hairs found in a crack on the inside of a 

windshield with limited occupants.)

11.4 Source factors that could decrease the significance of an association

11.4.1 Featureless hairs that lack pigmentation

11.4.2 Very dense pigmentation or opaque hairs, which inhibits the observation of microscopic 

characteristics

11.4.3 Damaged or very short hairs, which limit the number of characteristics that can be used for 

comparison

11.4.4 Known sample that has a large intra-sample variation (e.g., includes both pigmented and 

unpigmented hairs, includes a wide variety of dyed hairs)

11.5 Example Scenarios for Each Interpretation Category

The following examples are provided to assist in reaching each interpretation category. 

11.5.1 Physical Fit (not applicable)

11.5.2 Association with Highly Discriminating Characteristics

11.5.2.1 Behavioral factors and styling [e.g., a hair has been dyed several, distinctive colors multiple times 

and each color change is visible (at least on a microscopic level)]

11.5.2.2 Disease or hereditary condition that is manifest in hair
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11.5.2.3 External environmental factors observed in both the questioned hair and the known sample (e.g., 

putrefied roots, burnt hairs)

11.5.2.4 Substances on the surface of the hair in both the questioned and the known sample (e.g., topical 

treatments, paint, lice)

11.5.3 Association with Discriminating Characteristics

11.5.3.1 A hair with a range of macroscopic and microscopic characteristics that are included in the 

representative known sample. This can include microscopic color variation that reflects natural 

environmental exposures and conditions over time.

11.5.4 Association with Limitations

11.5.4.1 A hair that possesses a limited number of macroscopic and microscopic characteristics such as:

(1) a hair that is very short (if it possesses a limited number of macroscopic and microscopic 

characteristics);

(2) a hair that has little to no pigmentation either naturally or through artificial means (i.e., has 

very little or no pigmentation, generally possess fewer characteristics for comparison); or

(3) a hair that is heavily pigmented or heavily dyed (i.e., the hair appears opaque and therefore a 

limited number of characteristics are available for comparison).

11.5.5 Inconclusive

11.5.5.1 A questioned hair possesses similar characteristics to the known sample but also exhibits some 

differences. These differences can be attributed to post-depositional changes, the known sample 

not being representative of the source (does not contain the full range of characteristics), or 

because the questioned hair is from a different source.

11.5.6 Exclusion with Limitations

11.5.6.1 The questioned and known hairs possess different characteristics (e.g., cross-section, thickness 

variation, color, distribution of pigment). Due to the range of characteristics possible within an 

individual, an Exclusion (Elimination) is not possible.

11.5.7 Exclusion (Elimination)

11.5.7.1 The questioned and known hairs are grossly different in their macroscopic or microscopic 

characteristics (e.g., known consists of tightly curled, dark brown head hairs 3-5 inches long; the 

questioned hair is a straight blonde head hair 18 inches long).

11.6 Example Wording for Interpretation Categories

11.6.1 Physical Fit (not applicable)

11.6.2 Association with Highly Discriminating Characteristics

11.6.2.1 “Based on a visual and microscopical comparison, the characteristics observed in the Item 1 

questioned hair fall within the range of characteristics in the Item 2 known hairs. Items 1 and 2 

also possess distinctive characteristics that are indicative of (insert characteristic here, e.g., 

behavioral, disease/hereditary, or environmental characteristic) that is not typically or routinely 

observed in human hairs. Therefore, the source of Item 2 (person A) is included as a potential 
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source of Item 1 (Association with Highly Discriminating Characteristics). Microscopical hair 

comparisons are not a means of personal identification. The number of individuals that could be 

included as a possible source is unknown. These results should be evaluated in conjunction with 

DNA analysis.”

11.6.3 Association with Discriminating Characteristics

11.6.3.1 “Based on a visual and microscopical comparison, the characteristics observed in the Item 1 

questioned hair fall within the range of characteristics in the Item 2 known hairs. Therefore, the 

source of Item 2 (person A) is included as a potential source of Item 1 (Association with 

Discriminating Characteristics). Microscopical hair comparisons are not a means of personal 

identification. The number of individuals that could be included as a possible source is unknown. 

These results should be evaluated in conjunction with DNA analysis.”

11.6.4 Association with Limitations

11.6.4.1 “Based on a visual examination and microscopical comparison, the characteristics observed in the 

Item 1 questioned hair fall within the range of characteristics in the Item 2 known hairs. The 

source of Item 2 therefore cannot be eliminated as a potential source of Item 1; however, the 

characteristics for comparison are limited (Association with Limitations). The absence of a full 

range of physical and microscopic characteristics (insert limitation, e.g., hair too short, too little 

or no pigmentation, hair appears opaque, no root structure present) precludes a more definitive 

comparison result. Microscopical hair comparisons are not a means of personal identification. 

The number of individuals that could be included as a possible source is unknown. These results 

should be evaluated in conjunction with DNA analysis.”

11.6.5 Inconclusive

11.6.5.1 “Based on a visual and microscopical comparison between the Item 1 questioned hair and the 

Item 2 submitted known hairs, some similarities and some dissimilarities in the macroscopic and 

microscopic characteristics were observed. Therefore, no opinion can be reached as to whether or 

not the source of Item 2 (person A) can be included as a potential source of Item 1 

(Inconclusive). The comparison was limited due to (list limiting factors if applicable).”

11.6.6 Exclusion with Limitations

11.6.6.1 “Based on a visual and microscopical comparison between the Item 1 questioned hair and the 

Item 2 submitted known hairs, dissimilarities in the macroscopic and microscopic characteristics 

were observed. Based on the known sample submitted, Item 1 is not consistent with originating 

from the source of the Item 2 known hairs (Exclusion with Limitations). Assuming the known 

hair sample is representative, observations indicate that the hairs did not originate from the same 

source. Due to the natural variation that occurs in hairs, and the effect that time and environment 

can have upon a hair sample, these observed differences are insufficient for a definitive 

exclusion.”

11.6.6.2 “The Item 1 questioned hair was microscopically dissimilar to the Item 2 known head hair sample 

and, therefore, based on the known sample, is not consistent with originating from the same 

source (Exclusion with Limitations). This exclusion is limited because there was a significant 

time lapse between the collection of the questioned hair and the known sample (over 1 year). 

Due to the effect that time and environment can have upon a hair sample, these observed 

differences are insufficient for a definitive exclusion.”
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11.6.6.3 “One hair from Item 1 was examined with a compound microscope and exhibited characteristics 

consistent with a head hair of European ancestry. Item 1 was found to be microscopically 

dissimilar by comparison microscopy to the Item 2 known sample, also of European ancestry. 

Therefore, based on the known sample submitted, the source of the Item 2 hair sample cannot be 

included as a source of the questioned hair in Item 1 (Exclusion with Limitations). This 

exclusion is limited because there may be variation within the source that may not be represented 

in the known sample.”

11.6.7 Exclusion (Elimination)

11.6.7.1 “Based on a visual and microscopical comparison between the Item 1 questioned hair and the 

Item 2 submitted known hairs, gross dissimilarities in the macroscopic and microscopic 

characteristics (e.g., characteristics of ancestry) were observed. Therefore, the source of Item 2 

(person A) can be excluded as a potential source of Item 1 based on the submitted sample 

[Exclusion (Elimination)].”

11.7 Activity Level Considerations

11.7.1 Activity factors that could increase the overall significance of the association(s)

11.7.1.1 Large number of loose hairs transferred from a single source

11.7.1.2 A clump of hairs transferred from a single source

11.7.1.3 Cross-transfer of hairs between two people

11.7.1.4 Conditions that limit the possible sources of the hair (e.g., numerous hairs embedded in the 

interior surface of a broken windshield of a motor vehicle with known passengers)

11.7.1.5 The presence of hairs with stretched/anagen roots (hairs in the active growing phase) indicates the 

forceful removal of the hairs (although the amount of force cannot be determined).

11.7.2 Activity factors that could decrease the overall significance of the association(s)

11.7.2.1 The recipient works in a hair salon and is exposed on a regular basis to hairs with a wide variety 

of physical characteristics, hairs that could be forcefully removed, hairs that could have been 

naturally shed, and cut hair fragments.

11.7.2.2 Reasonable explanation for a transfer of hair(s) (e.g., two individuals living together)

11.7.3 Transfer and persistence 

11.7.3.1 Transfer and persistence factors are considered when evaluating questions about alleged activities 

and the presence of hair.

11.7.3.2 The retention of transferred hairs can depend upon the activity of the recipient object (e.g., 

person’s clothing, furniture) after the transfer. For example, hair on the clothing of a person who 

is moving around can be lost (fall off or transferred to another object) over time, while hair on a 

chair can remain there for a long period of time or could be transferred to the clothing of another 

person who sat on the chair subsequent to the original deposition of the hair.

11.7.4 Cross-transfers or multiple transfers

11.7.4.1 When there is a cross-transfer of hairs and each transfer individually results in an association, a 

statement regarding the significance of the cross-transfer can be reported separately.

11.7.4.2 In instances in which two or more associations are being reported (e.g., head and pubic hair, 
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multiple hairs), each association should be reported separately. Additional text can then be 

included describing whether and how the multiple reported associations could affect the overall 

significance assessment and opinions from the totality of the examination results.

11.7.5 Example Wording for Activity Level Considerations 

11.7.5.1 “A clump of hairs, similar in color, with stretched roots and adhering tissue/root sheath are 

indicative of the hairs having been forcibly removed.”

11.7.5.2 “Due to cohabitation of the involved individuals, a transfer of hair between these individuals 

would not be uncommon.”

11.7.5.3 Multiple transfers. “The presence of head and pubic hairs on the victim’s shirt similar to the 

known head and pubic hairs from the subject provides stronger support for contact having 

occurred between the victim and subject than either transfer alone.” 

11.7.5.4 Cross-transfer. “The presence of hairs on the victim’s shirt similar to the known hairs from the 

subject and the presence of hairs on the subject’s shirt similar to the known hair from the victim 

provides stronger support for contact having occurred between the victim and subject than either 

transfer alone.” 

12 Paint Reporting

12.1 Paint examination in forensic casework is typically a comparison of two or more paints, usually from 

a questioned source and a known source for the purpose of determining if the known source can be 

eliminated as a potential donor of the questioned paint. 

12.2 Analytical methodologies used for paint comparisons and discrimination studies have a direct impact 

on significance assessments. 

12.2.1 A Physical Fit can only be reported when there is alignment of two paint fragments along the 

broken edges, with a substrate where it was previously in contact, or through surface scratches and 

features that carry across onto the questioned chip from the remaining finish.

12.2.2 A comprehensive analytical scheme (see Guide E1610), unless sample size or condition prohibits 

it, includes visual and microscopical examinations to assess physical characteristics and 

instrumental analysis (see Guides E2808, E2809, E2937, WK74138, WK75180) to compare the 

organic and inorganic components of the paint layers.

12.2.2.1 A statement of decreased significance should be reported if a reduced analytical scheme was used 

to assess the physical and chemical characteristics that are routinely evaluated for samples of a 

given paint type (e.g., limitations of the sample size or condition, absence of equipment routinely 

used).

12.2.3 Increased or decreased significance is based on available information for the relevant population.

12.3 Source factors that could increase the significance of an association

12.3.1 Unusual physical or chemical features (e.g., surface damage)

12.3.2 Paint formulation applied for other than its intended use (e.g., architectural paint applied to a 

vehicle)

12.3.3 Paint with a known limited population (e.g., customized finishes)
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12.3.4 Increased number of layers

12.3.5 Unusual layer sequence where sequence order is typically controlled, mandated, or deliberate

12.3.6 For automotive paint, the following source factors could increase the significance of an association.

12.3.6.1 Repair during manufacture [original equipment manufacturer (OEM) repair]

12.3.6.2 Aftermarket refinish– number of layers and characteristics of the refinish affect association 

significance

12.3.6.3 Non-automotive paint layer within a layer system

12.3.6.4 Refinish layer(s) that change the topcoat color of the vehicle

12.3.7 For architectural paint, the following source factors could increase the significance of an 

association.

12.3.7.1 Multiple layers of various colors

12.3.7.2 Presence of inclusions, contaminants, or soil

12.3.7.3 Spray paint layer within a layer system

12.4 Source factors that could decrease the significance of an association

12.4.1 Limited number of analytical techniques used in the comparison

12.4.2 Limited number of features available for comparison

12.4.3 Condition of samples (e.g., mixed smears, contamination throughout the transferred material, 

minute sample amount)

12.4.4 Minor physical or chemical differences between items being compared that could be due to sample 

heterogeneity, contamination of the sample(s), or having a sample of insufficient size to adequately 

assess the homogeneity of the entity from which it was derived

12.4.5 Circumstances that increase the possibility of a random association (e.g., the suspect is a house 

painter and the material in question is an architectural paint)

12.5 Example Scenarios for Each Interpretation Category

The following examples are provided to assist in reaching each interpretation category.

12.5.1 Physical Fit

12.5.1.1 A Physical Fit is possible where there is alignment of a paint chip with another paint chip along 

its broken edge, with a substrate where it was previously in contact, or through corresponding 

individual characteristics (e.g., surface scratches) that carry across onto the questioned chip from 

the remaining finish.

12.5.2 Association with Highly Discriminating Characteristics

12.5.2.1 OEM automotive system with at least one aftermarket basecoat or primer layer above the original 

clear coat

12.5.2.2 OEM automotive system with two or more factory repairs (i.e., three or more total basecoatclearcoat sequences)

12.5.2.3 Architectural paint system with two or more different layers
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12.5.2.4 Automotive system with architectural paint present

12.5.3 Association with Discriminating Characteristics

12.5.3.1 Association of paint in which the typical analysis scheme was performed on mass-produced 

materials that have numerous features for evaluation (e.g., four-layered OEM automotive paint)

12.5.3.2 OEM automotive paint system with one factory repair of the same basecoat color and layer 

sequence (i.e., two total OEM basecoat-clearcoat sequences)

12.5.3.3 Single-layered paint for which there is knowledge of substantial discrimination power (e.g., red 

architectural paint) or product manufacturing distribution information that reduces the potential 

sources

12.5.3.4 Aftermarket refinish clearcoat and basecoat

12.5.4 Association with limitations

12.5.4.1 Smears with intermixing of layers that limit isolation of layers 

12.5.4.2 Limited physical features available for evaluation and no elemental analysis performed

12.5.4.3 Chips of an OEM automotive paint system containing only a clearcoat and an unremarkable 

basecoat (e.g., white color, acrylic melamine binder system with primarily titanium dioxide as an 

extender pigment)

12.5.4.4 Single-layered paint for which there is limited knowledge of discrimination power and product 

manufacturing distribution information (e.g., yellow tool paint)

12.5.5 Inconclusive

12.5.5.1 The paints exhibit both similarities and differences such that no opinion can be reached regarding 

an association or exclusion between items.

12.5.5.2 Suspected clearcoat automotive layer transfer in which both vehicles have consistent 

(indistinguishable) clearcoat chemistries

12.5.5.3 Additional peaks or relative intensities variations of peaks in the questioned paint could be 

components of the paint or contamination from a foreign material. Analysis of the transfer cannot 

differentiate whether the peaks are exclusionary or due to contamination (e.g., architectural paint 

transfer on a pry tool is intermixed with non-paint material, such as drywall).

12.5.6 Exclusion with Limitations

12.5.6.1 Vehicles can have different paint systems on different panels of the same vehicle. Therefore, it is 

possible that one known vehicle part differs from the questioned sample (e.g., one sample has an 

anti-chip layer). No analytical differences were observed in the corresponding layers. The vehicle 

is no longer available to collect an additional known sample.

12.5.7 Exclusion (Elimination)

12.5.7.1 Exclusionary difference in physical characteristics (e.g., different color, different layer structure)

12.5.7.2 Exclusionary difference in chemical composition (e.g., different binders or fillers present, 

different ratios/amounts of components that exceed the variation observed in the sample)

12.6 Example Wording for Interpretation Categories
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12.6.1 Physical Fit

12.6.1.1 “Examination and comparison of Items 1 and 2 revealed corresponding fracture contours, surface 

configurations, and layer structures. This provides extremely strong support for the proposition 

that the items originated from the same damaged source as opposed to the proposition they 

originated from different damaged sources (Physical Fit).”

12.6.2 Association with Highly Discriminating Characteristics

12.6.2.1 “Examination and comparison of the Item 1 questioned paint with Item 2 revealed they are 

consistent with respect to their observed and measured physical and chemical properties (e.g., 

layer sequence and chemical composition of corresponding layers) when analyzed using (insert 

analytical techniques here). It is therefore concluded that the Item 1 questioned paint recovered 

from the victim’s clothing corresponds to the Item 2 paint and therefore originated either from 

that vehicle or from another source of automotive paint having the same distinct characteristics 

(Association with Highly Discriminating Characteristics). This type of association was 

reached because the questioned and known paints both exhibit characteristics that are atypical of 

original equipment manufacturer (OEM) paints. Due to the presence of (insert feature here) it is 

unlikely that other vehicles produced at the same manufacturing plant in approximately the same 

time frame would also be indistinguishable. Furthermore, other vehicles painted in the same 

distinctive manner would have to be damaged and missing paint to be considered viable sources 

of the questioned paint.”

12.6.3 Association with Discriminating Characteristics

12.6.3.1 “Examination and comparison of the Item 1 questioned paint with Item 2 revealed they are 

consistent with respect to their observed and measured physical and chemical properties (e.g., 

layer sequence and chemical composition of corresponding layers) when analyzed using (insert 

analytical techniques here). It is therefore concluded that the Item 1 questioned paint recovered 

from the victim’s clothing corresponds to the Item 2 paint and therefore originated either from 

that vehicle or from another source of automotive paint having the same distinct characteristics 

(Association with Discriminating Characteristics). This type of association was reached 

because other vehicles produced at the same manufacturing plant and painted with the same type 

of paint system would also be indistinguishable. The techniques utilized in this comparative 

analysis can typically distinguish different paint systems.” 

12.6.3.2 “Examination and comparison of the Item 1 green questioned paint recovered from the clothing 

with the Item 2 can of spray paint revealed the paints are consistent with respect to their observed 

and measured physical and chemical properties (e.g., color, texture, and chemical composition) 

when analyzed using (insert analytical techniques here). It is therefore concluded that Item 1 

either originated from the Item 2 spray paint can or from another source of paint with the same 

distinct characteristics (Association with Discriminating Characteristics). This type of 

association was reached because spray paints are mass-produced, and other paint cans 

manufactured to the same specifications as Item 2 would also be indistinguishable from this paint. 

The techniques utilized in this comparative analysis can typically distinguish different spray paint 

products.”

12.6.4 Association with Limitations

12.6.4.1 “The Item 1 questioned paint recovered from the scene consists of a smear of (insert description). 

Examination and comparison of Item 1 with Item 2 revealed they are consistent in (color, general 
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binder type, etc.). Due to the limited quantity and abraded nature of the questioned sample, 

limited comparisons were performed. It is therefore concluded that Item 2 cannot be eliminated as 

a possible source of the questioned paint recovered from Item 1 (Association with Limitations). 

This type of association was reached due to the limited characteristics available for comparison 

due to the sample size and poor condition of the questioned sample.”

12.6.5 Inconclusive

12.6.5.1 “Examination and comparison of the Item 1 possible transfer on Vehicle 1 to the clearcoats of 

Vehicles 1 and 2 revealed that the vehicles have similar clearcoat chemical compositions to each 

other and to the possible transfer, and therefore, no opinion could be reached regarding an 

association or exclusion between the items (Inconclusive).”

12.6.6 Exclusion with Limitations

12.6.6.1 “Examination and comparison of the Item 1 questioned paint with Item 2 known paint from the 

left driver’s side door revealed they are different with respect to (insert characteristics here). The 

questioned paint did not come from the area of the vehicle where the known sample was taken 

(Exclusion with Limitations). Vehicles can have different paint layer systems on different panels 

of the same vehicle. Further comparisons can be performed if additional known samples are 

submitted.”

12.6.7 Exclusion (Elimination)

12.6.7.1 “Examination and comparison of the Item 1 questioned paint with Item 2 revealed they are 

different with respect to (insert characteristics here). It is therefore concluded that the questioned 

paint recovered from the scene did not originate from the reference area or panel of the vehicle 

represented by Item 2 [Exclusion (Elimination)].”

12.7 Activity Level Considerations

12.7.1 Activity factors that could increase the overall significance of the assessment(s)

12.7.1.1 The paint was applied wet to the surface (e.g., spray paint droplets) as opposed to being smeared 

on an item after the paint was dry.

12.7.1.2 Paint embedded in clothing rather than loosely adhered

12.7.1.3 Location or directionality of a transfer that assists in reconstruction of events (e.g., vehicle 

collision)

12.7.1.4 Cross-transfer of paints

12.7.2 Activity factors that could decrease the overall significance of the assessment(s)

12.7.2.1 Reasonable explanation as to why there was a transfer of paint(s) (e.g., individual was a painter 

with access to the location)

12.7.2.2 Environment with a high background of paint (e.g., busy intersection)

12.7.3 Transfer and persistence 

12.7.3.1 Transfer and persistence factors are considered when evaluating questions about alleged activities 

and the presence of paint.

12.7.3.2 Transferred paint can occur in different forms such as multilayered fragments, chips, abrasion 
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smears, dried stains, powder, or aerosol droplets. Paint can be recovered in varying sizes and 

amounts.

12.7.3.3 Paint is typically transferred by direct (primary) transfer; however, paint chips can be transferred 

by indirect (secondary, tertiary) transfer. The possibility of transfer depends on a variety of 

factors including, but not limited to, the surfaces involved in the contact, the nature of the contact, 

the duration of the contact, the condition of the paint, and the chemical composition of the paint.

12.7.3.4 Environmental degradation can also affect the degree of paint transfer. Flaking and chalking of 

paint increases the possibility of paint transfer during a contact.

12.7.3.5 The nature, duration, and intensity of contact affect the transfer of paint. In the case of 

multilayered painted surfaces, these factors can influence the number of layers transferred.

12.7.3.6 The potential for transferred paint to be lost as well as the rate of loss are dependent upon a 

number of factors including, but not limited to the form of the transferred material, the manner of 

transfer, the nature of the material containing the transfer, and activities which happen after 

contact occurred. For example, paint smears that are the result of impacts or wet applications of 

paint to a surface have a lower rate of loss, even with activity, whereas loose chips adhering to a 

surface are anticipated to have a higher rate of loss when post-transfer activity occurs.

12.7.4 Cross-transfers or multiple transfers

12.7.4.1 In instances in which two or more associations are being reported (e.g., cross-transfers or multiple 

transfers), each association should be reported separately. Then additional text can be included 

describing whether and how the multiple reported associations could affect the overall 

significance assessment from the totality of the examination results.

12.7.5 Example Wording for Activity Level Considerations 

12.7.5.1 “The physical characteristics of the paint on Item 1 establishes that the paint was dripped or 

splashed onto the surface rather than being brush-applied or transferred after it dried.”

12.7.5.2 Cross-transfer. “The presence of a three-layered paint chip on Vehicle A that is indistinguishable 

from the known paint from Vehicle B and a four-layered paint chip on Vehicle B that is 

indistinguishable from the known paint from Vehicle A provides stronger support for the transfer 

of paints between the two vehicles than either transfer alone.”

12.7.5.3 Multiple transfers. “The presence of a three-layered OEM paint chip on Vehicle A that is 

indistinguishable from the bumper paint from Vehicle B and a four-layered aftermarket paint chip 

on Vehicle A that is indistinguishable from the hood paint from Vehicle B provides stronger 

support for the transfer of paints from Vehicle B to Vehicle A than either transfer alone.”

13 Tape Reporting

13.1 Tape examination in forensic casework is typically a comparison of two or more tape pieces/rolls in 

an attempt to determine if they originated from different sources. If the samples cannot be eliminated 

as having come from the same roll, tape analysis can provide an assessment as to the significance of 

that association.
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13.1.1 For this guide, “tape” refers to pressure-sensitive tapes, primarily duct tape, electrical tape, and 

packaging tape, but this guide can also be applied to other types of tape.

13.2 Analytical methodologies used for tape comparisons have a direct impact on significance 

assessments. 

13.2.1 A Physical Fit can only be reported when there is alignment of ends or edges between two pieces 

of tape.

13.2.2 A comprehensive analytical scheme (see Guide E3260), unless sample size or condition prohibits 

it, includes visual and microscopical examinations to assess physical characteristics and 

instrumental examinations (see Guide E3085, WK74138, WK75180) to assess organic composition 

and inorganic (elemental) composition of the backing, adhesive, and reinforcing fibers (if 

applicable).

13.2.3 A statement of decreased significance should be reported if a reduced analytical scheme was used 

to assess the physical and chemical characteristics that are routinely evaluated for samples of a 

given tape type (e.g., limitations of the sample size or condition, absence of equipment routinely 

used).

13.2.4 Increased or decreased significance is based on available information for the relevant population.

13.3 Source factors that could increase the significance of an association

13.3.1 Unusual physical features, such as a printed backing

13.3.2 Manufacturing defects

13.3.3 Unusual chemical features, such as an uncommon filler

13.3.4 Unusual or rare type of tape (e.g., limited amount manufactured or limited distribution)

13.3.5 Environmental factors (e.g., weathering or damage) that would affect both the questioned and 

known tape 

13.3.6 Post-manufacturing modification of the tape observed on both samples being compared (e.g., 

handwriting on tape backing, paint overspray)

13.4 Source factors that could decrease the significance of an association

13.4.1 Common formulation of tape

13.4.2 Limited number of features available for comparison

13.4.3 Limited size

13.4.4 Contamination, degradation, or damaged condition of the sample(s)

13.4.5 Analytical scheme does not include an assessment of both the organic and inorganic/elemental 

composition of the tape

13.4.6 Analytical techniques do not include an assessment of all tape components

13.4.7 Minor physical or chemical differences between items being compared that could be due to sample 

heterogeneity, contamination of the sample(s), or having a sample of insufficient size to adequately 

assess the homogeneity of the entity from which it was derived

13.4.8 Circumstances that increase the possibility of a random association (e.g., limited number of 
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different products sold in a given area)

13.5 Example Scenarios for Each Interpretation Category

The following examples are provided to assist in reaching each interpretation category.

13.5.1 Physical Fit

13.5.1.1 A Physical Fit is possible where there is alignment of an end or edge of a piece of tape with 

another end or edge of a piece of tape or roll of tape, or through corresponding individual 

characteristics (e.g., surface scratches, fabric alignment) that carry across from one tape to the 

other.

13.5.2 Association with Highly Discriminating Characteristics

13.5.2.1 Post-manufacturing mark on the items (e.g., both known and questioned exhibit similar damage, 

handwriting on tape backing, paint overspray)

13.5.3 Association with Discriminating Characteristics

13.5.3.1 Association of tape in which the typical analysis scheme was performed on mass-produced 

materials that have numerous features for evaluation

13.5.3.2 A reduced analytical scheme was conducted, as long as the physical characteristics, organic 

composition, and inorganic/elemental composition of the tape were assessed to the extent possible 

(e.g., adhesives are too damaged to measure an accurate overall thickness).

13.5.4 Association with Limitations

13.5.4.1 Adhesive residue compared to a tape

13.5.4.2 No adhesive remaining on a tape backing

13.5.4.3 A reduced analytical scheme was conducted in which either the physical characteristics, organic 

composition, or inorganic/elemental composition of the tape were not satisfactorily assessed (e.g., 

no inorganic analysis of duct tape adhesives, no elemental analysis of electrical tape backings, no 

polarized light microscopy analysis of packaging tape backings)

13.5.4.4 Tape type for which there is limited knowledge of discrimination power and product 

manufacturing distribution information (e.g., office tape)

13.5.4.5 When the cause of minor physical or chemical differences between items being compared cannot 

be determined (i.e., the differences could be due to sample heterogeneity, contamination of the 

sample(s), or having a sample of insufficient size to adequately assess the homogeneity of the 

entity from which it was derived) but the samples are otherwise indistinguishable

13.5.5 Inconclusive

13.5.5.1 The questioned item is too damaged, degraded, or contaminated to conduct most examinations.

13.5.6 Exclusion with Limitations (not applicable)

13.5.7 Exclusion (Elimination)

13.5.7.1 Exclusionary difference in physical characteristics (e.g., different color, different layer structure)

13.5.7.2 Exclusionary difference in chemical composition (e.g., different elastomers or fillers present, 

different ratios/amounts of components that exceed the variation observed in the sample)
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13.6 Example Wording for Interpretation Categories

13.6.1 Physical Fit

13.6.1.1 “Based on distinct features of the torn edge of one end of the Item 1 piece of tape and the free end 

of the Item 2 roll of tape, Item 1 was observed to physically correspond with the end of Item 2. 

This provides extremely strong support for the proposition that Item 1 originated from and was at 

one time a part of Item 2 as opposed to the proposition that it originated from and was a part of 

another used roll (Physical Fit).

13.6.2 Association with Highly Discriminating Characteristics

13.6.2.1 “Items 1 and 2 were found to be indistinguishable in physical features and chemical composition 

(specify techniques). Further, both items have similar environmental damage on their surfaces. 

Therefore, Item 1 originated from Item 2 or another roll of damaged tape manufactured in the 

same manner (Association with Highly Discriminating Characteristics). This type of 

association was reached because other rolls of tape produced at the same manufacturing plant and 

with the same specifications would also be indistinguishable, but these rolls would not be 

expected to be damaged.”

13.6.3 Association with Discriminating Characteristics

13.6.3.1 “Items 1 and 2 were found to be indistinguishable in physical features and chemical composition 

(specify techniques). Therefore, Item 1 originated from Item 2 or another roll of tape 

manufactured in the same manner (Association with Discriminating Characteristics). This type 

of association was reached because other rolls of tape produced at the same manufacturing plant 

and with the same specifications would also be indistinguishable. Due to differences between tape 

products, the analytical techniques used in the analysis of these items allow for a high degree of 

discrimination.”

13.6.4 Association with Limitations

13.6.4.1 “The Item 1 residue is chemically indistinguishable (specify techniques) from the adhesive used 

in the Item 2 roll of tape. Therefore, Item 2 cannot be eliminated as a possible source of Item 1 

(Association with Limitations). This type of association was reached due to the limited number 

of characteristics available for comparison between the adhesive and the roll of tape, and because 

other rolls of tape have been manufactured (including rolls manufactured and distributed by other 

tape producers) that would have the same adhesive composition.”

13.6.5 Inconclusive

13.6.5.1 “Although there are some similarities between the Item 1 debris and the adhesive from the Item 2 

tape, severe contamination of Item 1 by biological fluids precludes a definitive assessment of the 

relationship between the debris and the tape. Therefore, no opinion can be reached regarding an 

association or exclusion between items (Inconclusive).”

13.6.6 Exclusion with Limitations (not applicable)

13.6.7 Exclusion (Elimination)

13.6.7.1 “Examination and comparison of the Item 1 piece of tape with the Item 2 roll of tape revealed 

they are different with respect to (insert characteristics here). It is therefore concluded that Item 1 

did not originate from Item 2 [Exclusion (Elimination)].”
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13.7 Activity Level Considerations

13.7.1 Multiple transfers

13.7.1.1 When two or more associations are being reported, each association should be reported 

separately. Additional text can then be included describing whether and how the multiple reported 

associations could affect the overall significance assessment from the totality of the examination 

results.

13.7.2 Example Wording for Activity Level Considerations

13.7.2.1 Multiple transfers. “Based on the reported results, more than one type of tape was recovered from 

and is indistinguishable between the various scenes. These findings could increase the 

significance of the reported results.”

14 Keywords 

14.1 trace evidence; interpretation; reporting results; report wording; fiber; glass; hair; paint; tape

15 References

1.  Trejos, T., Koch, S., Mehltretter A., “Scientific foundations and current state of trace evidence - a 

review,” Forensic Chemistry, Vol. 18, 2020, 100223. 

2.  Weis, P., Dücking, M., Watzke, P., Menges, S., and Becker, S., “Establishing a match criterion in 

forensic comparison analysis of float glass using laser ablation inductively coupled plasma mass 

spectrometry,” Journal of Analytical Atomic Spectrometry, Vol. 26, No. 6, 2011, pp. 1273-1284. 

3.  Dorn, H., Ruddell, D. E., Heydon, A., and Burton, B. D., “Discrimination of float glass by LA-ICPMS: assessment of exclusion criteria using casework samples,” Canadian Society of Forensic Science 

Journal, Vol. 48, No. 2, 2015, pp. 85-96. 

4.  Hoffman, T., Corzo, R., Weis, P., Pollock, E., van Es, A., Wiarda, A. W., Stryjnik, A., Dorn, H., 

Heydon, A., Hoise, E., Le Franc, S., Huifang, X., Pena, B., Scholz, T., Gonzalez, J., and Almirall, J., 

“An Inter-Laboratory Evaluation of LA-ICP-MS Analysis of Glass and the Use of a Database for the 

Interpretation of Glass Evidence,” Forensic Chemistry, Vol. 11, 2018, pp. 65-76. 

5.  Ryland, S., “Discrimination of Flat (Sheet) Glass Specimens Having Similar Refractive Indices Using 

Micro X-Ray Fluorescence Spectrometry” Journal of the American Society of Trace Evidence 

Examiners, Vol. 2, No. 1, 2011, pp. 2-12.