OSAC 2022-S-0015 Standard Guide for 

Forensic Physical Fit Examination

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OSAC 2022-S-0015

Standard Guide for 

Forensic Physical Fit 

Examination

Trace Materials

Chemistry: Trace Evidence Scientific Area Committee

Organization of Scientific Area Committees (OSAC) for Forensic Science
OSAC 2022-S-0015 Standard Guide for 

Forensic Physical Fit Examination

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Draft OSAC Proposed Standard

OSAC 2022-S-0015 

Standard Guide for

Forensic Physical Fit Examination

Prepared by 

Trace Materials Subcommittee

Version: 1.0

December 2021

Disclaimer:

This OSAC Proposed Standard was written by the Trace Materials Subcommittee of 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.

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. 
OSAC 2022-S-0015 Standard Guide for 

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1 Standard Guide for Forensic Physical Fit Examination 

2 1. Scope

3 1.1 This guide covers the forensic physical fit examinations for the macroscopical and microscopical 

4 examinations of broken, torn, or separated materials for the purpose of determining whether or not they 

5 at one time formed a single item. This guide is intended as an overview of the physical fit examination of 

6 these materials and to assist individuals in the evaluation and documentation of their physical 

7 comparisons.

8 1.2 The forensic examiner considers sample composition, condition (e.g., size, environmental effects, wear, 

9 complexity of separated edge features) when selecting procedures that are suitable for each specific case.

10 1.3 This standard is intended for use by competent forensic science practitioners with the requisite formal 

11 education, discipline-specific training (see Practice E2917), and demonstrated proficiency to perform 

12 forensic casework.

13 1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included 

14 in this standard.

15 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is 

16 the responsibility of the user of this standard to establish appropriate safety, health and environmental 

17 practices and determine the applicability of regulatory limitations prior to use. 

18 1.6 This international standard was developed in accordance with internationally recognized principles on 

19 standardization established in the Decision of Principles for the Development of International Standards 

20 issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. 

21

22 2. Referenced Documents 

23 2.1 ASTM Standards:

24 C1256 Practice for Interpreting Glass Fracture Surface

25 E1459 Guide for Physical Evidence Labeling and Related Documentation

26 E1492 Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Laboratory

27 E1610 Guide for Forensic Paint Analysis and Comparison

28 E1732 Terminology Relating to Forensic Science

29 E2225 Guide for Forensic Examination of Fabrics and Cordage

30 E2917 Practice for Forensic Science Practitioner Training, Continuing Education, and Professional 

31 Development Programs

32 E3260 Guide for Forensic Examination and Comparison of Pressure Sensitive Tapes

33

34 2.2 Other Documents:

35 ISO/IEC 17025 (2017) General Requirements for the Competence of Testing and Calibration Laboratories

36 OSAC Guide for Interpretation and Reporting in Forensic Comparisons of Trace Materials

37

38 3. Terminology

39 3.1 Definitions – For additional terms commonly employed for general forensic examinations see E1732 and 

40 for fractography see C1256.

41 3.2 Definitions of Terms Specific to This Standard:

42 3.2.1 arrest lines, n – a sharp line on the fracture surface defining the crack front shape of an arrested or 

43 momentarily-hesitated crack. (1)

44 3.2.2 fractography, n – the means and methods for characterizing fractured specimens or compounds (1)

45 3.2.3 individual characteristics, n – the attribute(s) that establish(es) a single source. 

46 3.2.3.1 Discussion: other terms used include random accidental characteristics, randomly 

47 acquired characteristics, distinguishing characteristics.

48 3.2.4 physical fit, n – an association based upon the realignment of two or more fragments or pieces that 

49 demonstrate they were once joined together to form a single object.

50 3.2.4.1 Discussion - The term match (e.g., physical match, fracture match) is not recommended 

51 to be used as it can be misleading to the layperson.
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52 3.2.5 scarp, n -A line on the crack surface, which is the locus of intersection of a liquid-filled part of a 

53 running crack front with an unwetted part, or a moist part with a dry part (2).

54 3.2.6 technical review – a qualified second party’s evaluation of reports, notes, data, and other 

55 documentation to ensure there is appropriate and sufficient support for the actions, results, 

56 conclusions, opinions, and interpretations (OSAC Preferred Term – Lexicon).

57 3.2.7 verification, n—provision of objective evidence that a given item fulfils specified requirements. ISO 

58 9000:2017(E)

59

60 4. Summary of Guide

61 4.1 Physical fit examination is the process of evaluating two or more samples to determine if they were at 

62 one time a single unit. It is based on the premise that separation events (e.g., breaks, cuts, tears) are not 

63 reproducible because of the combination of applied forces, construction features, and material 

64 properties.. When something is broken, torn, or separated, the surfaces or edges of adjacent fragments 

65 often have observable features that correspond with one another. These complementary features, patterns, 

66 and edges produced during separation allow an examiner to recognize and reconstruct samples that were 

67 at one time a single unit or attached to one another.

68 4.2 Physical fit examinations can involve the assessment or reassembly of multiple pieces prior to the 

69 comparison of a questioned sample to a possible known source.

70 4.3 Separation occurs in a variety of ways (e.g., broken, cut, torn). Separated materials that possess irregular 

71 edges and individual characteristics on their complementary surfaces can be realigned to demonstrate 

72 they were at one time a single unit. The physical fit can be viewed in two or three dimensions.

73 4.4 The absence of edge detail or material loss does not always rule out the possibility of a physical fit. A 

74 physical fit could result when physical features align across the separation boundary (e.g., striations, 

75 wood grain). 

76 4.5 Different types of materials exhibit differing types of individual characteristics based on their 

77 construction, chemical structure, and physical properties. The recognition and distinction between class 

78 and individual characteristics for differing types of materials allows the use of the same general 

79 procedures for the physical fit examinations of all materials.

80 4.6 This guide contains a general procedure to perform physical fit examinations as well as a summary of 

81 considerations and limitations for an examiner to evaluate when conducting these examinations.

82

83 5. Significance and Use

84 5.1 This guide can assist the examiner in selecting and organizing a general analytical scheme for the 

85 evaluation and documentation of physical comparisons of materials for a potential physical fit. The type 

86 and size of material influences the exact steps and equipment needed to assess the physical fit. The 

87 evaluation, documentation, and interpretation are all important parts of a physical fit examination. 

88 5.2 This guide addresses special considerations for physical fit analysis for glass, skeletal material, polymers, 

89 tapes and textiles. 

90 5.3 Physical fit examinations have a long history of use in forensic science as described in Brooks et al (3). 

91 This reference and Section 18 include studies on the fractography of different materials and the use of 

92 physical fit examinations in forensic casework..

93 5.4 It is not the intention of this guide to present comprehensive theories regarding the mechanism of 

94 fractures, tearing, cutting, or other methods of separation. This information is available from training 

95 courses and reference materials such as ASTM Guide C1256 and others (2, 4 – 8). 

96 6. Quality Assurance Considerations

97 6.1 A quality assurance program is used to assess and verify that analytical testing procedures and reporting 

98 of results are monitored by means that include, but are not limited to, proficiency tests and technical 

99 audits. General quality assurance guidelines are available in ISO/IEC 17025. 

100 7. Apparatus and Materials 

101

102 7.1 Different equipment is used depending on the material being examined and the case specifics. 

103 7.2 General list of common materials utilized:
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104 7.2.1 Camera

105 7.2.2 Stereomicroscope

106 7.2.3 Comparison microscope

107 7.2.4 Magnifier

108 7.2.5 Polarizing filters

109 7.2.6 Light box

110 7.2.7 Oblique lighting

111 7.2.8 UV lighting

112 7.2.9 Clay

113 7.2.10 Casting material

114 7.2.11 Plastic sheets

115 7.2.12 Solvents 

116 7.2.13 Ruler

117 7.2.14 Micrometer

118 7.2.15 Sample handling tools (e.g., probe, forceps) 

119 7.2.16 Packaging and documentation materials (e.g., labels, markers)

120

121 8. Sample Handling

122

123 8.1 The general handling and tracking of samples should meet or exceed the requirements of Practice E1492 

124 and Guide E1459.

125 8.2 The need for multiple types of examinations (e.g., other trace, DNA, latent prints, firearms) is considered 

126 before initiating a physical fit examination. Communicate with examiners from other disciplines to 

127 coordinate the order of examination or evidence preservation and recovery methods.

128 8.3 Physical fit examinations typically require that samples from more than one item of evidence be examined 

129 together. Documentation practices provide records of where samples came from and their condition as 

130 received in the laboratory. Document physical damage or the presence of other evidence. Documentation 

131 includes images, diagrams, non-destructive marking/labeling of the individual samples, or other methods 

132 deemed appropriate for the evidence in question. 

133 8.3.1 Samples should each be uniquely identified prior to analysis. 

134 8.4 A preliminary examination of the samples is performed prior to bringing them into contact with each other 

135 to prevent cross-contamination. 

136 8.5 The areas to be compared are carefully handled to protect them from damage or alteration.

137 8.6 Alterations made to the evidence during the examination are documented.

138 8.7 All tools used are cleaned prior to contact with the evidence.

139 8.8 WARNING: Some samples have sharp edges and caution is warranted when handling these samples.

140 8.9 Following the examination, evidence is repackaged in a manner as to protect the evidence against damage.

141

142 9. General Considerations and Limitations 

143

144 9.1 General Considerations:

145 9.1.1 The plasticity of the object should be taken into consideration, especially in areas where stretching 

146 caused by the separation could cause distortion in a physical fit. Notes should include a discussion 

147 of apparent missing material and deformation of material that could impact results.

148 9.1.2 Features that carry across the separation boundary (e.g., scratches, stains, manufacturing defects) 

149 can serve to demonstrate the physical fit.

150 9.1.3 The separation method (e.g., cut, torn) can be assessed during the physical fit assessment; however, 

151 that is outside the scope of this guide. 

152 9.1.4 Physical fit examination is a visual technique and therefore bias could occur. Precautions to 

153 minimize bias include:

154 9.1.4.1 Receiving adequate training 

155 9.1.4.2 Avoiding contextual bias (e.g., suspect’s confession, investigator’s opinions)

156 9.1.4.3 Assessing questioned samples prior to comparison to known samples

157 9.1.4.4 Employing a quality assurance program

158 9.1.4.5 Conducting technical review and verification
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159 9.1.5 An error rate has not yet been established for physical fit examinations due to the complexity of the 

160 associated variables (e.g., variety of materials, different breaking mechanisms).

161 9.1.6 In the absence of a physical fit, a sample cannot be associated with an individual source. A class 

162 association can be determined but that is outside the scope of this guide. 

163 9.2 Limitations

164 9.2.1 Sample composition or condition could limit the evaluation of a physical fit examination. Examples 

165 include but are not limited to:

166 9.2.1.1 Size

167 9.2.1.2 Environmental effects

168 9.2.1.3 Wear

169 9.2.1.4 Deformation or stretching before separation 

170 9.2.1.5 Lack of features to compare along the separated edge(s)

171 9.2.1.6 Improper collection, preservation, or handling

172

173 10. General Procedure

174 10.1 Refer to Section 8 for sample handling considerations prior to and during physical fit examinations.

175 10.2 A typical scheme for physical fit examinations is outlined in Figure 1.

176 10.3 During the examination, questioned samples should be assessed prior to comparison to known samples. 

177 10.4 When exclusionary differences are observed at any point during the examination, no further 

178 examinations are required. Exclusionary differences can include differences in class characteristics (e.g., 

179 two pieces of tape with different construction or a red shirt with a piece missing compared to a blue 

180 piece of fabric). 

181 10.5 When the general contours do not align and there are no corresponding features on the separated 

182 surfaces or no traversing surface features, no further physical fit examinations are required. Additional 

183 physical and chemical analysis could be completed and are outside the scope of this guide.

184 10.6 Imaging, sketching, or written notes, or any combination thereof, is used to document features. See 

185 Section 12 for additional detail on Examination Documentation.

186 10.7 A macroscopic assessment is conducted of the samples of interest.

187 10.7.1 The condition, general features, and properties of the samples are examined. Features such as 

188 material type, color, shape, construction features, curvature, fluorescence, surface features, 

189 texture, grain, weave, orientation, and degree of gloss are observed and documented. These 

190 features can be examined with various light sources at varying angles of illumination. The 

191 material of interest dictates what properties are present and relevant during the physical 

192 assessment.

193 10.7.1.1 Samples that are suitable for physical fit examination have features that are not 

194 noticeably obstructed by extensive distortion, wear, weathering, or loss of material.

195 10.7.1.2 If the samples are deemed suitable for fit comparison, the samples are compared side by

196 side and the macroscopic edge features are observed.

197 10.7.2 The macroscopic features on the separated edges, such as the presence of layers, continuous 

198 construction or manufacturing marks, fracture marks, alignment of the fracture pattern, color, 

199 dimensions, stains, or pattern continuation are observed and documented.

200 10.7.3 The dimensions of the questioned and known samples, in addition to the area of the alignment, 

201 can be measured (e.g., using a ruler, caliper, micrometer) and documented.

202 10.8 When individual characteristics are not visible at the macroscopic level to determine and demonstrate a 

203 physical fit, detailed observation at the microscopical level follows.

204 10.9 A microscopical examination is conducted on the samples of interest.

205 10.9.1 The microscopic edge features are observed using a simple magnifier, stereomicroscope, 

206 comparison microscope, or a combination of magnification types. Different light sources could 

207 be used depending on the type of material being examined (e.g., annular ring light, fiber optic 

208 light, transmitted, reflected). The size and physical properties of the examined samples determine 

209 which magnification type should be used.

210 10.9.2 The questioned and known edges are compared microscopically for the observation and 

211 documentation of similarities and differences in features such as alignment, fracture pattern 

212 features, stretching, distortion, fracture marks, pigmentation, grain, texture, weave, twist, 
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213 fluorescence, and missing material. Minimizing contact between the sample edges can prevent 

214 damage or contamination during alignment.

215 10.9.3 Optional: The portions of the edges that align across the samples (e.g., duct tape scrim edges) are 

216 measured and documented. 

217 10.10 A physical fit occurs when the samples share class and individual macroscopic and microscopic features 

218 across the edges and surfaces, including the cross section. 

219 10.11 The samples or documentation of features are submitted for verification, technical review or both.

220 10.12 The correspondence of observed class characteristics between the compared items during a physical fit 

221 examination could warrant additional testing to evaluate the possibility of an association of the evidence 

222 with class characteristics or an exclusion (elimination). When further examinations are conducted, refer 

223 to appropriate ASTM standards (e.g., E1610, E2225) as well as the OSAC Guide for Interpretation and 

224 Reporting in Forensic Comparisons of Trace Materials. 

225

226 11. Special Considerations

227

228 11.1 The types of materials listed below are commonly encountered for physical fit; however, this does not 

229 preclude other materials from being examined and compared for physical fit. For each material, class 

230 characteristics including composition or construction, the manner of separation, relevant features, and 

231 limitations inherent to that material are considered. Different materials will exhibit varied individual 

232 characteristics based on their construction and chemical structure (amorphous, crystalline, fibrous or 

233 combinations thereof) or their properties (brittle or ductile). The recognition and distinction between 

234 class and individual characteristics for different materials allows the use of the same general procedures 

235 for the physical fit examinations of all materials.

236

237 11.2 Glass

238 11.2.1 Background: Glass exhibits brittle behavior at room temperature. Therefore, broken glass is 

239 particularly well suited to reassembly to its original configuration because there is usually no 

240 distortion caused by the breaking event (1). Objects broken by brittle failure such as glass 

241 could be distinguished by ductile or viscous failure in that its fragments could fit together 

242 exactly. The reassembled object will have the same shape as before the breaking event. For a 

243 more detailed description of glass fractography, see ASTM C1256, (1) and (2).

244 11.2.2 Separation methods: The breaking of glass objects deforms elastically (i.e., reversibly) under 

245 an applied load until the onset of cracking, at which time the deformation is permanent (2). In 

246 every case, the fracture begins at a particular site (i.e., origin of impact) and grows from there. 

247 Cracks could develop slowly over a period of time or rapidly. Crack development is 

248 dependent upon numerous factors including glass type, loading pressure, impact type (i.e., 

249 high velocity or low velocity), humidity. (2).

250 11.2.3 Relevant features: A glass physical fit examination involves conducting an examination of 

251 fracture surfaces for features such as rib marks, including arrest lines, Wallner lines, hackle, 

252 and scarps. Surface features, curvature, material type, color, thickness, and fluorescence are 

253 observed to determine if all pieces could be from a single object. Surface features are used to 

254 place all the fragments in the same orientation (e.g., fluorescent side facing up, surface 

255 scratches). 

256 11.2.4 Other considerations: There are no published studies addressing minimum lengths of fractured 

257 edges suitable for physical fit determinations. However, successful results from proficiency 

258 testing have been documented for glass fragments as small as approximately 5mm (9).

259 11.2.5 Other limitations: 

260 11.2.5.1 Brittle fracture examinations could be severely restricted due to improper collection 

261 and preservation at the scene or during shipping.

262 11.2.5.2 Glass could shatter into multiple pieces rather than separating into only two 

263 pieces. In this case, reconstruction of pieces from a single evidentiary sample could be 

264 performed prior to a physical fit examination
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265 11.2.5.3 Tempered glass objects could leave fewer discriminating fracture features to 

266 conduct a physical fit examination due to the breaking mechanism. However, the fit 

267 becomes more distinctive when multiple pieces of tempered glass fit together. 

268

269 11.3 Skeletal Material

270 11.3.1 Background: Physical fit examinations for skeletal material are generally conducted to 

271 reconstruct fragments in order to identify the origin of bone fragments, to conduct trauma 

272 examination, or to conduct morphological or metric assessment for biological profile 

273 estimations. In rare cases, however, a comparison between two items is conducted, such as in 

274 cases where material is recovered from distinct spatial locations, or at distinct temporal 

275 periods. In these cases, application of the results and interpretation terminology in this 

276 guideline could be appropriate.

277 11.3.2 Separation methods: The pattern of alterations to fresh bone depends upon the type of stress

278 applied to the material. Application of a low-velocity impact could lead to permanent plastic 

279 deformation of the material prior to material failure (fracture), leading to warping of the 

280 material. Higher velocity impact (e.g., gunshots) could cause material failure without prior 

281 plastic deformation. For dry bone (postmortem alterations), plastic deformation generally 

282 does not occur prior to breakage, potentially allowing easier reconstruction.

283 11.3.3 Relevant features: Physical features of skeletal material are assessed at a macroscopical level 

284 and microscopical level, as appropriate. Relevant features include alignment of separated 

285 edges, and consistency of both external compact bone and internal trabecular bone patterns.

286 11.3.4 Other considerations: Consideration should be given to the possibility that separated portions 

287 of skeletal material could undergo differing taphonomic processes after separation (e.g., 

288 differential weathering, burning).

289 11.3.5 Other limitations: Limitations include edge wear from mishandling or taphonomic processes,

290 plastic deformation of fresh bone, and non-distinctive fracture or breakage patterns.

291

292 11.4 Synthetic Polymers 

293 11.4.1 Background: Synthetic polymers are manufactured materials that are found in a variety of 

294 consumer and industrial products and are commonly encountered as items of evidence. For 

295 purposes of physical fit examination, synthetic polymers are classified as either “rigid” or 

296 “flexible”.

297 11.4.1.1 Examples of rigid polymers include plastic vehicle parts, automotive paint chips, 

298 closed-cell foams, and other rigid polymeric materials excluding glass (See Glass 

299 section above).

300 11.4.1.2 Examples of flexible polymers include plastic bags, garbage bags, cling film, some 

301 architectural paint, open cell foams, and other flexible polymeric materials excluding 

302 tape (See Tape section below). 

303 11.4.2 Separation methods: The fracture behavior of a polymer is determined by the absence of 

304 appreciable plastic deformation prior to failure (i.e., brittle fracture) or the presence of plastic 

305 deformation prior to failure (i.e., ductile fracture). Rigid polymers most often experience 

306 “brittle” fracture, while flexible polymers most often experience “ductile” fracture. This is 

307 due to their intrinsic properties (e.g., size, shape, composition, and degree of crystallinity). 

308 However, external factors (e.g., temperature, state of wear, presence of existing damage, and 

309 amount, type, and orientation of applied stress) could cause variation in the brittle/ductile 

310 fracture behavior of a polymeric material.

311 11.4.2.1 Examples of the external factors that commonly cause fracture in rigid polymers 

312 include motor vehicle collision, bullet penetration, and blunt impact of a 

313 weapon/tool. 

314 11.4.2.2 Examples of the external factors that commonly cause fracture in flexible polymers 

315 include cutting, tearing, shearing with a dispenser, or a combination of these.

316 11.4.3 Relevant features: Physical features of rigid and flexible synthetic polymers are assessed at a 

317 macroscopical level and microscopical level, as appropriate.

318 11.4.3.1 Relevant features in rigid polymer physical fit examinations include layer structure 

319 (including the substrate when present), hackle marks, pre-existing scratches or 
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320 cracks across the separation boundary, contour, curvature, and texture. The three321 dimensional structure of a fractured polymer is valuable in a physical fit 

322 comparison.

323 11.4.3.2 Relevant features in flexible polymer physical fit examinations include color, size, 

324 perforation pattern, construction (if applicable), texture, print, and contour. Class 

325 characteristics imparted during manufacturing (e.g., striations, pigment bands, and 

326 interference colored bands), individual characteristics (e.g., fisheyes, arrowheads, 

327 streaks, tiger stripes, and surface scratches) or both which cross the separation 

328 boundary could demonstrate a physical fit (10). 

329 11.4.4 Other considerations:

330 11.4.4.1 Rigid polymers could shatter into multiple pieces rather than separating into only 

331 two pieces. In this case, reconstruction of pieces from a single evidentiary sample 

332 could be performed prior to a physical fit examination.

333 11.4.4.2 Coatings or other materials with multiple layers could separate along the physical 

334 boundary between layers.

335 11.4.4.3 Rigid polymers fatigue over time due to exposure to physical stressors, 

336 environmental conditions, or both. Cracks could form in a polymer due to fatigue 

337 and could alter how easily the polymer fractures, the location of a future fracture, or 

338 both.

339 11.4.4.4 The use of a light box as well as polarizing films could assist with visualization of 

340 some of the relevant features in flexible polymer physical fit examinations, 

341 including interference colors.

342

343 11.4.5 Other limitations:

344 11.4.5.1 Flexible polymers can easily deform when they are rolled, stretched, or twisted. 

345 When performing a physical fit examination, the amount of deformation could 

346 negatively impact the ability to align two or more pieces.

347 11.4.5.2 Sometimes when flexible polymers are cut, there are insufficient individual 

348 characteristics visible to determine a physical fit.

349

350 11.5 Tape 

351 11.5.1 Background: There are a variety of tape products available in the market, and tape evidence 

352 could include one or more classes of tape. Tapes have at least two layers, a backing and a 

353 pressure-sensitive adhesive (PSA), formulated to meet the tape’s specific end-use. Some tapes, 

354 such as duct tapes, also contain a fabric reinforcement layer. The physical structure and 

355 chemical composition of tape influences the relevant features of the material for physical fit 

356 examinations; however, a more detailed discussion of the classes of tape and their components 

357 is found elsewhere (ASTM E3260) and is outside the scope of this guide.

358 11.5.2 Separation Methods: Tapes are typically separated from the main source either by tearing 

359 sections by hand or using teeth, or cutting the tape with scissors, knife, tape dispenser, or other 

360 sharp tool. However, fragments of tape could also be separated during an explosion or other 

361 high impact event.

362 11.5.3 Relevant features for physical fit examinations of tapes:

363 11.5.3.1 The relevant features for physical fit examinations are dependent on the class of 

364 tape involved. Generally, the presence of letters or patterns or other manufacturing 

365 marks on tape samples could be relevant in the side-by-side comparison of tape 

366 evidence for physical fits.

367 11.5.3.2 Macroscopic features to observe include color, shape, construction features, 

368 surface features, external marks or debris, texture, weave, orientation, and degree 

369 of gloss. The general torn edge appearance is also a relevant feature, and could 

370 include straight, angled, wavy, or patterned edges.

371 11.5.3.3 Microscopic features of the separated edges include manufacturing marks or 

372 calendaring striations in alignment across the edges, areas where there is alignment 

373 in the respective tape layers, and areas of parallel protrusions or indentations 

374 across edges. Protruding scrim fibers could be observed in tapes that possess them.
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375 11.5.3.4 To facilitate verification, the portion of the edge that aligns across the items should 

376 be measured (e.g., relative length, qualitative or quantitative descriptors, 

377 photographs with scale) and documented (11, 12). 

378

379 11.5.4 Other considerations:

380 11.5.4.1 When used in the commission of a crime, tape is typically placed down on various 

381 substrates such as paper, wood, metal, or skin. There is also potential for the tape 

382 to adhere to itself. When collected, residues, leftover material, or additional forms 

383 of trace evidence (fibers, soil, etc.) from the original substrate could remain on the 

384 adhesive side of the tape. These residues could obstruct or interfere with the 

385 examination and documentation of features. In those situations, the examiner could 

386 attempt to separate the tape from the extraneous material using warm air, liquid 

387 nitrogen, a freezer, or solvents. However, the examiner should be careful to gently 

388 separate the tape under magnification to avoid damaging the ends or destroying 

389 features needed for physical examination.

390 11.5.4.2 The presence and orientation of reinforcing material (such as in duct, cloth, or 

391 filament tapes) could be used to orient and compare similar items.

392 11.5.4.3 Some kinds of tape could feather at the edges, where only portions of the layers 

393 can separate, leaving microscopic features that are unlikely to be randomly 

394 reproduced.

395 11.5.4.4 Physical fit determinations of some tapes (e.g., duct tapes with thicker adhesives) 

396 can be facilitated by removing some of the adhesive layer. To prevent the 

397 distortion of the edge features and scrim alignment, part of the adhesive is 

398 carefully removed until the scrim fibers are visible. 

399 11.5.5 Other limitations:

400 11.5.5.1 Some classes of tape are more likely than others to deform from stretching 

401 (electrical tape) or to have loss of material (masking tape). In addition, tapes with 

402 fewer layers do not have as many potential features to observe for physical fit 

403 comparisons.

404 11.5.5.2 In an explosion, fire, or high-impact event, fragments of tape could be lost, 

405 preventing a full comparison for physical fits.

406 11.5.5.3 Tape samples without the full width of tape present could limit physical fit 

407 evaluations.

408

409 11.6 Textiles

410 11.6.1 Background: Textiles are comprised of natural or manufactured fibers subjected to a variety 

411 of manufacturing processes (e.g., spinning, weaving, knitting) to produce complex 

412 materials such as cordage and fabric. Although on a basic level all textiles are formed 

413 from fibers, the final product can vary in color, construction, and composition. Physical 

414 fit assessments could be performed in cases where pieces of damaged cordage or 

415 fabric are recovered from various locations. 

416 11.6.2 Separation Methods: Textile physical fits occur when cordage or fabric has 

417 been mechanically damaged through cutting, tearing, or a combination of both, and the 

418 resulting pieces/edges are realigned. The separation process is dependent on the mechanical 

419 properties as well as the type and orientation of stress being applied. Distinct characteristics 

420 such as a neat and straight severance (typically associated with cutting damage) or a 

421 ragged/irregular severance (typically associated with tearing damage) could assist with 

422 physical fit examination. 

423 11.6.3 Relevant features: Physical features of a textile are assessed at the fabric/cordage level, 

424 yarn level and fiber level, as appropriate. Textile features include size, shape, 

425 construction, yarn and fiber characteristics, stitched edges, selvedges, color, patterns, stains, 

426 unusual stretching or contours, and damage. In addition to general features such as pattern 

427 and color, mechanical separation of textiles typically results in a series of long and 

428 short yarns/fibers which could be used to orient and physically align the textiles of 

429 interest. Following the physical alignment, these “longs and shorts” are examined to ensure 
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430 that their relative positions along the damaged edges of two or more textile pieces 

431 correspond. 

432 11.6.4 Other Considerations: Textiles are flexible materials that can be rolled, stretched, and 

433 twisted. Orientation of the textile at the time of damage could impact the location, 

434 pattern and type of mechanical separation incurred. Additionally, when the elasticity limit of 

435 the textile is exceeded, permanent deformation could occur. When performing a textile 

436 physical fit examination, these deformations could impact the ability to align two or 

437 more damaged textile pieces. 

438 11.6.5 Other Limitations: Sometimes the ability to perform textile physical fit assessments 

439 on damaged textiles is limited by laundering/handling/distorted threads, contaminants such 

440 as blood, stretching or distortion of the textile during damage, and general wear effects.

441 12. Examination Documentation 

442

443 12.1 Documentation includes written notes, photography, diagrams, non-destructive marking/labeling of the 

444 individual items, or other methods deemed appropriate for the evidence in question.

445 12.2 Documentation should include observations of physical damage and the presence of other evidence.

446 12.3 Written descriptions, sketches, photographs, or other images are used to document each sample’s 

447 features. Close-up images or photomicrographs are used to document the microscopic features.

448 12.4 Physical fits of evidential value require documentation of a sufficient quality for technical review, 

449 verification, court presentations, or other visual demonstrations. This includes images of pertinent edges 

450 and observed features as well as the correspondence between the edges of the pieces showing the 

451 physical fit.

452 12.5 At minimum, written documentation of no physical fits are also required.

453 12.6 Additional documentation (e.g., sketches) or images should be taken to facilitate note taking.

454 12.7 Images should contain a scale. If not practicable, the image is annotated with the magnification used.

455 12.8 The examination notes shall contain sufficient detail to support the interpretations and opinions such 

456 that another qualified practitioner could fully evaluate the details of the examination and consideration 

457 of limitations, and thus be able to evaluate the quality of the interpretation and opinion based on those 

458 notes or documentation.

459 12.9 Verification of the actual evidence by a second, qualified examiner is completed when sufficient 

460 documentation of the physical fit is not possible. The verification is documented in the case record. 

461

462 13. Results and Interpretations

463 The following results and interpretations can be reached with regards to physical fit evaluations:

464

465 13.1 Physical Fit

466 13.1.1 The items that have been broken, torn, separated, or cut exhibit physical features that realign in 

467 a manner that is not expected to be replicated. A physical fit can result when features realign 

468 along the compared edges or when features do not realign along the compared edges but there 

469 are physical features present (e.g., striations, wood grain) which carry across the separation 

470 boundary and can themselves be realigned. 

471 13.1.1.1 Physical Fit is the highest degree of association between items. It is the opinion that

472 the observations provide the strongest support for the proposition that the items 

473 originated from the same source as opposed to the proposition they originated from 

474 different sources. 

475 13.1.1.2 A Physical Fit is not currently based upon statistically-derived measurements; it is 

476 also not based upon exhaustive comparisons to all potential sources.

477

478 13.2 No Physical Fit

479 13.2.1 The items correspond in observed class characteristics, but exhibit physical features that do not 

480 realign, or they realign in a manner that could be replicated. 

481 13.2.2 Alternatively, the items can exhibit physical features that partially realign, display 

482 simultaneous similarities and differences, show areas of discrepancy (e.g., warped areas, 
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483 burned areas, missing pieces), or have insufficient individual characteristics that hinder the 

484 ability to determine the presence or absence of a physical fit. 

485 13.2.3 The absence of a physical fit does not imply that the compared items did not originate from the 

486 same source. 

487 13.2.4 The presence of partial fit features can increase the significance of the finding in cases where 

488 the items are associated with class characteristics during additional testing.

489 13.2.5 When no physical fit is observed and additional trace material examinations are completed, 

490 refer to OSAC Guide for Interpretation and Reporting in Forensic Comparisons of Trace 

491 Materials. 

492 13.2.6 When the physical fit examination is the terminal examination step, a statement is included 

493 explaining the reasons for not completing further examinations.

494 13.2.7 The two items did not originate from the same source (exclusion) when the items exhibit 

495 differences in their class characteristics. 

496

497 14. Report wording examples

498 Additional examples of report wording can also be found in the OSAC Guide for Interpretation and Reporting 

499 in Forensic Comparisons of Trace Materials.

500

501 14.1 Physical Fit

502 14.1.1 Based on distinct features of the torn edge of one end of the Item 1 piece of tape and the free 

503 end of the Item 2 roll of tape, Item 1 was observed to physically correspond with the end of 

504 Item 2. This provides extremely strong support for the proposition that Item 1 originated from 

505 and was at one time a part of Item 2 as opposed to the proposition that it originated from and 

506 was a part of another used roll (Physical Fit).

507 14.1.2 The Item 1 piece of tape and the free end of the Item 2 roll of tape physically corresponded 

508 with distinct features of the torn edges. This serves as the basis for the opinion that Item 1 and 

509 Item 2 were once part of a single unit (Physical Fit).

510

511 14.2 No Physical Fit

512 14.2.1 The Item 1 car piece from the scene was examined and compared to the Item 2 bumper. The 

513 Item 1 car piece and the Item 2 bumper were similar in general appearance but did not 

514 physically fit back together (No Physical Fit). They do however share sufficient class 

515 characteristics to warrant additional comparison examinations to evaluate the possibility of an 

516 association with class characteristics or an exclusion.

517 14.2.2 The Item 1 and Item 2 pieces of plastic do not realign to form one larger piece (No Physical 

518 Fit). However, they do share sufficient class characteristics to warrant additional comparison 

519 examinations to evaluate the possibility of an association of evidence with class characteristics 

520 or an exclusion. The results of those examinations will be reported separately.

521 14.2.3 The Item 1 metal tip exhibited physical features that generally align with the Item 2 broken 

522 knife, however, there were also areas of discrepancy. Due to these similarities and differences, 

523 no physical fit was determined (No Physical Fit). They do however share sufficient class 

524 characteristics to warrant additional comparison examinations to evaluate the possibility of an 

525 association with class characteristics or an exclusion.

526 15. Verifications/Technical review

527 15.1 Physical fits are verified by another qualified examiner. Unless deemed necessary based on case details, 

528 a second examiner does not need to verify physical fits that are observed within an item or between 

529 items from the same location. Other results (e.g., inconclusive, exclusion) may also be verified.

530 15.2 Verification can be in the form of review and independent examination of the actual evidentiary 

531 material or by reviewing the photographs or images taken of the evidence.

532 15.3 Verification documentation includes the specific items examined, the result, verifier’s initials, and the 

533 date.
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534 15.4 Verification can be completed during the technical review process.

535

536 16. Additional Considerations

537 16.1 During a physical fit examination, it is possible to encounter items with features that join or realign in 

538 a manner that could be replicated.

539 16.1.1 Examples of this type of evidence include vehicle parts that snap together (e.g., mirror and 

540 mirror assembly), electrical components (e.g., USB drive and port), a pen and cap, or clothing 

541 items separated at the seam (e.g., coat and sleeve without tearing of the fabric).

542 16.1.2 Items which join or realign in this manner demonstrate class characteristics which are alike, 

543 but do not have a separation boundary and edge features to compare and evaluate as with 

544 physical fit determinations

545 16.1.3 Report wording example.

546 16.1.3.1 The Item 1 mirror from the scene was examined and compared to the Item 2 mirror 

547 housing to determine whether at one time they could have been connected. Based 

548 on the examinations conducted, they are able to be joined; however, there are no 

549 individual characteristics present. Therefore, these items could have been at one 

550 time connected, or they each could have been connected to other similar objects.

551 16.1.4 Additional examinations could be conducted on items that join or realign in this manner; 

552 however, these examinations are specific to the material and are beyond the scope of this 

553 guide.

554

555 17. Keywords

556 Physical fit, physical match, fracture match, fracture fit

557

558 18. References

559

560 (1) Quinn GD. Fractography of Ceramics and Glasses, NIST Special Publication, 960-16e2, May 2016.

561 (2) Frechette VD. Failure Analysis of Brittle Materials, Advances in Ceramics, Vol 28, Westerville, Ohio: 

562 Wiley-American Ceramic Society, 1990.

563 (3) Brooks E, Prusinowski M, Gross S, Trejos T. Forensic physical fits in the trace evidence discipline: a 

564 review. For Sci Int Vol 313, 2020. https://doi.org/10.1016/j.forsciint.2020.110349. 

565 (4) Becker WT, Shipley RJ. ASM Handbook, Volume 11: Vol. 11: Failure Analysis and Prevention. Materials 

566 Park, Ohio: ASM International, 2002.

567 (5) Hull D. Fractography: observing, measuring and interpreting fracture surface topography. Cambridge, 

568 U.K.: Cambridge University Press, 1999.

569 (6) Glass Fractures, Scientific Working Group for Materials Analysis, Forensic Science 

570 Communications, Volume 7, No 1, January, 2005.

(7) Hearle JWS, Lomas B, and Cooke WD. Atlas of Fibre Fracture and Damage to Textiles 2nd 571 Edition Boca 

572 Raton, LA: CRC Press 2000.

573 (8) Taubin JM, Adof FP, Robertson. Examination of Damage to Textiles in: J. Robertson, M. Grieve (Eds.), 

574 Forensic Examination of Fibres, Second ed., London: Taylor & Francis, 1992.

575 (9) http://forensic-testing.net/system/files/fts-13-pm_summary.pdf (accessed 03/27/2020).

576 (10)Von Bremen UG, Blunt LKR. Physical Comparison of Plastic Garbage Bags and Sandwich Bags, J For 

577 Sci, Vol 28, No 3, July 1983, pp. 664-654.

578 (11)McCabe KR, Tulleners FA, Braun JV, Currie G, Gorecho EN. A quantitative analysis of torn and cut duct 

579 tape physical end matching, J For Sci 58 (2013) S34–S42.

580 (12)Prusinowski M, Brooks E, Trejos T. Development and validation of a systematic approach for the 

581 quantitative assessment of the quality of duct tape physical fits, For Sci. Int. 307 (2020). 

582