OSAC 2022-S-0030 Standard for 

Methodology in Bloodstain Pattern Analysis

1

OSAC 2022-S-0030 

Standard for Methodology 

in Bloodstain Pattern 

Analysis

Bloodstain Pattern Analysis

Physics / Pattern Interpretation Scientific Area Committee

Organization of Scientific Area Committees (OSAC) for Forensic Science
 OSAC 2022-S-0030 Standard for 

Methodology in Bloodstain Pattern Analysis

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Draft OSAC Proposed Standard

OSAC 2022-S-0030 Standard

for Methodology in 

Bloodstain Pattern Analysis

Prepared by 

Bloodstain Pattern Analysis

Version: 1.0 - OSAC Open Comment

March 2022

Disclaimer:

This OSAC Proposed Standard was written by the Bloodstain Pattern Analysis 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.
 OSAC 2022-S-0030 Standard for 

Methodology in Bloodstain Pattern Analysis

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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-forensicscience/scientific-technical-review-panels. 
 OSAC 2022-S-0030 Standard for 

Methodology in Bloodstain Pattern Analysis

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1 1. Introduction

2 In this document, the following verbal forms are used: “shall” indicates a requirement, “should” 

3 indicates a recommendation; “may” indicates permission; and “can” indicates a possibility or 

4 capability. 

5 2. Scope

6 2.1 This document covers the process of examining bloodstains and bloodstain patterns 

7 to determine the significance of their presence or absence, what potential forces or 

8 mechanisms could result in those bloodstains or bloodstain patterns, and the significance 

9 of those determinations in regard to the scope or reason for the examination.

10 2.2 This document will address when to classify but not how to classify.

11 2.3 This document will not address documentation, preservation, or collection at the 

12 scene or on items of evidence.

13 3. Normative References 

14 There are no normative reference documents. Annex A, Bibliography, contains informative 

15 references.

16 4. Terms and Definitions

17 For the purposes of this document, the following terms and definitions apply.

18 4.1 Analyst: An individual trained and competent to carry out the step described 

19 4.2 Assumptions: Something supposed as true, without adequate supporting evidence or 

20 certain knowledge.

21 4.3 Cognitive Bias: A set of influences that may affect the reliability and validity of 

22 one’s observations and conclusions.

23 4.4 Event Segment: Time snapshots depicted by moments of activity. 

24 4.5 Examination: The act or process of observing, searching, detecting, recording, 

25 prioritizing, collecting, analyzing, measuring, comparing, and/or interpreting.

26 4.6 Interpretation: Explanations for the observations, data, and calculations.

27 4.7 Mechanism: The action or event process resulting in a bloodstain or bloodstain 

28 pattern.

29 4.8 Observed Data: Any demonstrable information observed within a bloodstain or 

30 bloodstain pattern that an examiner relies upon to reach a decision, interpretation, or 

31 opinion.
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32 4.9 Opinion: View, judgement, or belief that takes into consideration other information 

33 in addition to observations, data, calculations, and interpretations.

34 4.10 Post-incident Artifact: Any alteration to a bloodstain or bloodstain pattern resulting 

35 from the actions of first responders, medical personnel, or an individual occurring after 

36 the creation of that bloodstain or bloodstain pattern.

37 4.11 Task-irrelevant information: Information that is not necessary for drawing 

38 conclusions about the propositions in question, or if it assists only in drawing conclusions 

39 from something other than the physical evidence designated for testing or assists only in 

40 drawing conclusions by some means other than an appropriate analytic method.

41 4.12 Task-relevant information: Information that is necessary for drawing conclusions 

42 about the propositions in questions, from the physical evidence that has been designated 

43 for examination, or through the correct application of an accepted analytic method by a 

44 competent analyst.

45 4.13 Utility: The usefulness of a bloodstain or bloodstain pattern for a further step in the 

46 analysis.

47 5. Requirements

48 Prior to the start of analysis, the purpose and scope of the investigation and questions to be 

49 answered should be defined, as well as the information available to be utilized. List all these 

50 source materials. If a customer has made a request for analysis, this shall be included in the case 

51 documentation. 

52 Bloodstain pattern analysts will be exposed to various sources and types of information 

throughout their analysis which may be task-relevant or task-irrelevant. 53 1 When considering how 

54 this information can influence their decision-making, they must consider and document the 

55 potential for cognitive bias. Where possible, this methodology follows linear sequential 

unmasking – expanded.2 56 The analyst shall access information in the following order prescribed 

57 by the methodology. If information is accessed out of order, it shall be documented.

58 If the request is to evaluate a written statement, the bloodstain pattern analysis shall be 

59 completed prior to reading the statement. Once complete, the opinions rendered can be compared 

60 to support or refute the statements made. 

1 National Commission on Forensic Science, Ensuring the forensic analysis is based upon task-relevant 

information. It is available at https://www.justice.gov/archives/ncfs/page/file/641676/download

2 Dror, Itiel E, and Jeff Kukucka. “Linear Sequential Unmasking-Expanded (LSU-E): A general approach 

for improving decision making as well as minimizing noise and bias.” Forensic science international.

Synergy vol. 3 100161. 13 Aug. 2021. It is available at https://doi.org/10.1016/J.FSISYN.2021.100161.
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61 A request for analysis may be undefined, where much is unknown. In these cases, the analyst 

62 shall render opinions based upon the quality and quantity of the information available for 

63 analysis. 

64 Some inquiries may not be answerable through bloodstain pattern analysis. 

65 5.1 Observation and Data Collection:

66 The analyst shall utilize imaging (e.g., photographs, 3D-laser scanning) and notes to 

67 document observations of bloodstained items, areas, and voids to characterize stain and 

68 pattern size, shape, distribution, appearance, and location. Sketches or diagrams may also 

69 be utilized to aid documentation. It is understood that imaging may be provided to the 

70 analyst or produced by the analyst. 

71 5.1.1 Locate all areas where blood is present.

72 5.1.2 Locate all areas where blood is notably absent.

73 5.1.3 Characterize stain and pattern sizes. 

74 5.1.3.1 If measuring individual stains, measure in millimeters.

75 5.1.3.2 For spatter stains, sizes of stains refer to the widths.

76 5.1.3.3 For non-spatter stains, sizes refer to overall dimensions.

77 5.1.3.4. Measurements for the overall dimensions of the stains grouped 

78 into patterns may also be documented. 

79 5.1.4 Characterize stain and pattern shapes.

80 5.1.4.1 Circular

81 5.1.4.2 Elliptical

82 5.1.4.3 Irregular

83 5.1.4.4 Linear or curvilinear

84 5.1.4.5 Edge characteristics, to include observable characteristics such as 

85 clearly defined sharp edges, spines, feathering, etc.

86 5.1.5 Characterize stain distribution

87 5.1.5.1 Stain arrangement: radiating, linear, curvilinear

88 5.1.5.2 Size distribution within a pattern

89 5.1.5.3 Angle of impact distribution (directionality)
 OSAC 2022-S-0030 Standard for 

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90 5.1.5.4 If stains within a pattern converge to an area

91 5.1.5.5 2D or 3D deposition - e.g., located on the top surface only or 

92 penetrating the target substrate

93 5.1.6 Characterize stain and pattern appearance in terms of:

94 5.1.6.1 Coloration, dilution, thickness 

95 5.1.6.2 Degree of wet, dry, flaking

96 5.1.6.3 Clotted

97 5.1.6.4. Altered

98 5.1.6.5 Flow, gravity effects

99 5.1.6.6 Impression patterns: Friction ridge detail, footwear

100 5.1.6.7 Vacuoles and mucous strands

101 5.1.6.8 Repeating pattern of the same characteristics

102 5.1.7 Characterize the surface the stains are present on. 

103 5.1.7.1 Fixed versus moveable objects 

104 5.1.7.2 Porous, non-porous

105 ● Construction and materials of fabrics and textiles

106 5.1.7.3 Smooth, irregular, textured, treated, flexible, etc. 

107 5.1.7.4 Curved, flat, angled

108 5.1.8 Document other observable material e.g., tissue, hair, bullet holes

109 5.2 Designate areas of blood into groupings of stains/patterns. 

110 5.2.1. Organize patterns by stain size, shape, distribution, appearance, and 

111 location.

112 5.2.2 Not all bloodstains can be organized into patterns because their observable 

113 characteristics do not provide enough information to proceed.

114 5.2.3 Determine the utility of bloodstains or bloodstain patterns. A utility 

115 determination can be decided based on a multitude of reasons.

116 5.2.3.1 The observed characteristics of the bloodstains and bloodstain 

117 patterns may have ambiguous information that can be attributed to 
 OSAC 2022-S-0030 Standard for 

Methodology in Bloodstain Pattern Analysis

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118 multiple pattern types and the determination is made that a meaningful or 

119 helpful interpretation is not possible based on the scope of the request.

120 5.2.3.2 The lack of quantity of stains present may not allow the analyst to 

121 definitively exclude any mechanism or make any meaningful 

122 interpretation. 

123 5.2.3.3 The bloodstains or bloodstains patterns may exhibit 

124 characteristics of alteration to an extent that the original deposition cannot 

125 be reliably interpreted.

126 5.2.3.4 The bloodstains or bloodstain patterns may be deposited on a 

127 surface that would result in unreliable characteristics leading to unreliable 

128 interpretations due to the interaction that the blood and target surface 

129 would have.

130 5.2.3.5 The bloodstains or bloodstain patterns appear to be overlapping in 

131 such a way that it cannot be reliably determined which stains are 

132 associated and which stains are not associated. 

133 5.2.4 The analyst should be able to justify why a stain/pattern has not been 

134 classified. The value and potential significance of these stains/patterns will be 

135 assessed based upon the scope and purpose of the investigation. 

136 5.3 Classification of Patterns from Observable Characteristics

137 Classification of bloodstains and bloodstain patterns is the process that utilizes 

138 observable characteristics to include those mechanisms that cannot be excluded, 

139 resulting in an interpretation. At this step/stage the analyst shall only use observable 

140 stain(s) and pattern characteristics to make their initial interpretation(s). 

141 5.3.1 The analyst should consider potential mechanisms or means of 

142 deposition that can be excluded. The analyst shall then note all pattern types that 

143 will be given further consideration during the refinement process. Pattern types 

144 can be assigned based on mechanism or force and can be as definitive as using 

145 the ASB BPA terminology or generally describing a mechanism or force (e.g. 

146 Passive, gravity, airborne, or transfer) 

147 5.3.2 When applicable, the analyst should determine which collected samples 

148 will be submitted for additional forensic analysis (e.g., amylase testing). Forensic 

149 analysis may assist in refinement of the pattern classification and the logical 

150 exclusion of mechanisms. 

151 5.3.3 Where applicable, the analyst may utilize methods to apply to pattern areas 

152 to aid in determining flight path characteristics, area of origin, area of 

153 convergence, etc.

154 5.4 Refinement of Interpretations applying Task-Relevant Contextual Information
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155 Refinement is the logical exclusion of pattern types included in the interpretations above 

156 with the addition of forensic biology/DNA, and medical/pathology reports. This 

157 refinement is only relevant when assessing whether to exclude impact, expiration, 

158 forward and backspatter, or projected patterns. Examples of refinement which can be 

159 made based on review of this task-relevant contextual information:

160 ● If there is no pathological evidence of a gunshot injury, backspatter and 

161 forward spatter may be excluded as possible pattern types.

162 ● There is no evidence of blood in the airway from medical reports and/or 

163 alpha-amylase testing is negative, expiration may be excluded as a 

164 possible pattern type.

165 5.4.1 The analyst shall only consider information relevant to source and/or 

166 blood-letting injuries necessary for pattern interpretation refinement. The analyst 

167 shall document and apply this information to eliminate pattern types not 

168 supported by blood-letting injuries. 

169 5.4.2 Considering the results of the forensic analysis, the analyst should refine 

170 the previously documented list of potential mechanisms or means of deposition 

171 and further exclude any pattern types that are no longer logical given the results.

172 5.4.3 If the reliability of any piece of this contextual information is questioned, 

173 the analyst shall return to the interpretations prior to refinement.

174 5.4.4 An analyst shall not include a pattern type if it is not supported by the 

175 observed data regardless of contextual information.

176 5.5 Event Reconstruction

177 Event reconstruction in bloodstain pattern analysis is the process of incorporating and 

178 assimilating all observed data and interpretations to begin to determine the possible scene 

179 events that created the pattern(s)/stain(s). All outcomes at this step are termed to be 

180 interpretations. The interpretations may be generic (e.g. an impact occurred in this 

181 location or a transfer pattern is located on the floor) or specific to the case (e.g. a gunshot 

182 wound was created in this location or a bloody footwear impression is located on the 

183 floor). Reconstruction of events are first addressed in finite periods of time or event 

segments 184 3 where specific patterns may be associated with specific events. It is also 

185 possible for these event segments to be sequenced relative to one another as part of the 

186 event reconstruction. It is understood that not every event segment can be determined 

187 and therefore, it is not expected that every stain or pattern can be or needs to be 

188 interpreted.

189

3 Gardner, R., 2018. Practical crime scene processing and investigation. Third edition. CRC Press.
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190 Each interpretation involves the generation of a hypothesis and testing the hypothesis by 

191 considering other possibilities and either eliminating them or refining the original 

192 hypothesis to include them.

193 The analyst may apply case-specific, task-relevant information to inform their bloodstain 

194 pattern interpretations. The analyst shall document when the contextual information was 

195 accessed.

196 Examples of contextual information include 

197 ● First responder actions

198 ● Investigative reports

199 ● Other relevant forensic reports (e.g., footwear comparison, patent latent 

200 print comparison)

201 5.5.1 Where applicable and possible, the analyst shall make interpretations in 

202 regard to the following with the understanding that not every stain or pattern 

203 needs to be interpreted as stated above:

204 5.5.1.1 Interrelationship(s) of stains(s) and pattern(s) based on their 

205 locations. (e.g., satellite patterns adjacent to projected patterns or impact 

206 patterns on adjacent walls in a corner of a room). This interrelationship 

207 can be based on the physical proximity of two or more patterns, 

208 recognized repeating patterns throughout the scene, or potential 

209 correlating mechanisms of patterns.

210 5.5.1.2 Directionality of stains and patterns based upon their shapes and 

211 characteristics (e.g., within swipe and wipe patterns)

212 5.5.1.3 Potential sources of blood that contributed to stains or patterns 

213 such as wounds, pools, and objects containing blood which may be 

214 responsible for stains and patterns. Where possible, correlate potential 

215 blood sources to stains and patterns with potential location of sources 

216 during the mechanistic event (e.g., incorporating area of origin 

217 calculations to wound locations). Where applicable, source associations 

218 shall incorporate results from available DNA reports to further aid in 

219 determining sources.

220 5.5.1.4 Sequencing the order of deposition of stains and patterns

221 5.5.1.5 Voids and how they may have been created (e.g., limiting angles)

222 5.5.1.6 Repositioned objects/movement using voids or flow patterns

223 5.5.1.7 Identifying patterns that could potentially be pre- or post-incident 

224 artifacts (e.g., Insect stains, stains that appear to be very old, or medical 

225 personnel attempts to aid the victim)
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226 5.5.1.8 Potential influence of environmental factors on blood deposition 

227 and patterns (e.g., temperature, humidity, or altered stains)

228 5.5.1.9 Indications of time since deposition (e.g., perimeter stains, 

229 coloration, or serum separation)

230 5.5.2 Concurrent with 5.5.1, the analyst shall determine and document all 

231 assumptions made and limitations that may have influenced interpretation.

232 Examples:

233 ● Only one source of blood at the crime scene.

234 ● Only Person X has injuries consistent with a projected blood source.

235 ● Analysis was performed completely from photographic documentation 

236 without attending the crime scene.

237 ● The deposition of all bloodstains occurred contemporaneous to the 

238 bloodletting event(s) in question.

239 ● Possible scene alteration is present from medical intervention.

240 ● Clean-up activities occurred.

241 ● Analysis was performed from photographs only and was limited to the 

242 documentation provided. 

243 5.6. Final Opinion (Case Conclusion in Report writing doc)

244 Assigning significance to interpretations

245 5.6.1 Upon completing and reporting all interpretations, the analyst, where 

246 applicable, should render a final opinion regarding the initial request or 

247 investigative questions. This opinion shall not use any unsubstantiated data (see 

248 Report Writing doc).

249 5.6.2 In cases where the request for bloodstain pattern analysis includes a specific 

250 question (e.g., homicide or suicide) or statement analysis (e.g., the suspect 

251 provides a statement on what happened, and bloodstain pattern analysis is used to 

252 support or refute such statements) the analyst must evaluate all proposed 

253 possibilities and document and report support for and support against each one. 

254 In some cases, the analyst may determine and propose that another possibility has 

255 more support based on the evidence and interpretations. In such cases, the 

256 analysis must document and report the basis of the proposed possibility.

257

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263

264

265
 OSAC 2022-S-0030 Standard for 

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266 Annex A

267 (informative)

268

269 Bibliography

270

271 1] Dror, Itiel E, and Jeff Kukucka. “Linear Sequential Unmasking-Expanded (LSU-E): A 

272 general approach for improving decision making as well as minimizing noise and bias.” 

273 Forensic science international. Synergy vol. 3 100161. 13 Aug. 2021. It is available at 

274 https://doi.org/10.1016/J.FSISYN.2021.100161. 

275

276 2] Gardner, R., 2018. Practical crime scene processing and investigation. Third edition. CRC 

277 Press.

278

279 3] National Commission on Forensic Science, Ensuring the forensic analysis is based upon 

280 task-relevant information. It is available at 

281 https://www.justice.gov/archives/ncfs/page/file/641676/download