Scientific Working Group on Bloodstain Pattern Analysis:  Admissibility Resource Kit on Bloodstain Pattern Analysis

Scientific Working Group on Bloodstain Pattern Analysis (SWGSTAIN)


To provide a resource to prepare for admissibility hearing on the topic of blood stain pattern analysis (BPA).


The Scientific Working Group on Bloodstain Pattern Analysis (SWGSTAIN) comprises BPA experts from North America, Europe, New Zealand, and Australia. SWGSTAIN provides a professional forum in which practitioners in BPA and related fields can discuss and evaluate methods, techniques, protocols, quality assurance, education, and research. SWGSTAIN’s ultimate goal is to use these professional exchanges to address substantive and operational issues within the field of BPA and to work to build consensus-based, or “best practice,” guidelines for the enhancement of the discipline of BPA.

Statement of Purpose

Admissibility standards being applied to forensic science disciplines are creating new challenges for the individual analysts when providing expert witness testimony.  The analysts are being held to a higher standard in justifying the science of their respective disciplines.

The Admissibility Resource Kit (ARK) is a repository of pertinent information designed to primarily assist Bloodstain Pattern Analysts in preparing for evidence admissibility hearings. The information contained herein consists of general & foundational text, listed documents, related internet website links, predicate questions, and visual aids that serve as an effective educational tool. The layered or nested formatting of this information will hopefully provide a progressive learning vehicle that will help educate the end-user on the critical elements that should be mastered to articulate the underlying scientific principles of the Bloodstain Pattern Analysis discipline.

The following is a collection of information pertaining to the admissibility of bloodstain pattern analysis evidence. This collection of resources is not all-inclusive but rather represents significant research, legal opinions, challenges, rulings and other issues related to the discipline.

Foundational Overview of Bloodstain Pattern Analysis

BPA is a field of study that relies on the fact that blood is a fluid, and as such, it adheres to physical laws. Therefore, bloodstain patterns are broadly predictable and reproducible under similar conditions. BPA is the study of the size, shape, distribution, and location of bloodstains in order to establish the physical events that gave rise to their origin. BPA is the scientific study of the static consequences resulting from dynamic bloodshedding events and the physical properties of blood in motion. The study involves detecting, describing, and analyzing the size, shape, distribution, number, location, and pattern of bloodstains, as well as the nature of their target surfaces and the relationship among various bloodstains at the scene. Potential target surfaces include virtually any surface capable of sustaining detectable bloodstains—for example, the victim, the victim’s clothing, the suspect, the suspect’s clothing, any weapon(s), any vehicle(s), or any other surfaces, such as walls, floors, or ceilings.

BPA applies mathematics and scientific principles from biology and physics (e.g., trigonometry, characteristics of blood, fluid dynamics, force/acceleration, surface tension, cohesive forces). Its practice, therefore, embraces methods that are characteristic of the natural sciences.

The purpose of the scientific study of BPA is to provide information about the bloodshedding events that produced patterns on the targets under investigation. This purpose may include providing insight(s) into (a) the position of the victim(s) at the time of bloodshed, (b) the position of the subject(s), (c) the origin(s) of the bloodstains, (d) the sequence of events that created the patterns, (e) the movement(s) of the victim, suspect, or objects at the scene during and after bloodshed, (f) the agreement or disagreement of these bloodstains with statements provided by the victim(s), suspect(s), or witness(es), etc.

Admissibility Standards

A list of significant court decisions is provided here that address the admissibility of expert scientific evidence and testimony.


Frye v. United States, 54 App. D.C. 46, 293 F. 1013, 1014 (1923)

The Frye ruling was established in 1923 under the case of Frye v. United States. It relates to expert testimony being admissible only if the principles on which it was based have been "generally accepted" as reliable by the relevant scientific community.

Frye-based admissibility proceedings seek to:

1.   Determine if the expert testimony will assist the jury in trying the case;

2.   Establish that the expert testimony is based upon scientific principles that have been widely accepted in the field;

3.   Establish that the witness is qualified as an expert in the relevant field and;

4.   Establish the credibility of the witness.

Federal Criminal Code and Rules, Title 28, Section VII, 702 (1975)

Federal Rule 702- Testimony by Experts    Notes
In 1973 (revised Dec. 1, 2011) Federal Rules of Evidence were adopted by the federal courts system.  Rule 702 broadly governs the admissibility of expert testimony, didn’t mention general acceptance, but stated:

1.   Determine that the testimony is based upon sufficient facts or data;

2.   Determine that the testimony is a product of reliable scientific principles and methods and

3.   Determine that the witness has applied the scientific principles and methods reliably to the facts of the case.

Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993)

 The Daubert ruling was established in 1993 under the case of Daubert v. Merrell Dow Pharmaceuticals, Inc. It relates to expert testimony and how the judge should determine the validity of the expert witness. There are five guidelines which a judge can use to help guide their decision. Not all of these specific Daubert factors can apply to every type of expert testimony.

Daubert-based admissibility proceedings seek to:

1.   Provide evidence that the methodology has been tested;

2.   Provide evidence that the methodology has been subjected to peer review and publication;

3.   Determine the  known or potential error rate associated with the theory or technique when applied;

4.   Provide evidence that standards controlling the technique are in place and maintained;

5.   Provide evidence that the methodology has been generally accepted by the relevant scientific community.

Although these criteria were not meant as a checklist, they are being applied in this way. If one of these criteria is not met, then the testimony may be found to be inadmissible.

Precedent Cases by State (coming soon)

BloodstainCase Rulings by State


Expert evidence must be necessary in order to allow the fact finder:

1.    to appropriate the facts due to their technical nature, or;

2.    to allow for a correct judgment on a matter if ordinary persons are unlikely to do so without the assistance of persons with special knowledge.

R. v. Mohan [2 S.C.R. 9] 1994
Admission of expert evidence depends on the application of the following criteria:

    1. relevance;

    2. necessity in assisting the trier of fact;

    3. the absence of any exclusionary rule;

    4. a properly qualified expert

R. v. D.D. [Supreme Court of Canada] 2000
"The application of the four Mohan criteria is case-specific.  Determinations of relevance and necessity, as well as the assessment of whether the prejudicial effect of the evidence outweighs its probative value, must be made within the factual context of the trial."

Per Major J., 46 "The second requirement of the Mohan analysis exists to ensure that the dangers associated with expert evidence are not lightly tolerated.  Mere relevance or "helpfulness" is not enough.  The evidence must also be necessary."

"A fortiori, a finding that some aspects of the evidence "might reasonably have assisted the jury" is not enough.  As stated by Sopinka et al., expert evidence must be necessary in order to allow the fact finder: (1) to appreciate the facts due to their technical nature, or; (2) to form a correct judgment on a matter if ordinary persons are unlikely to do so without the assistance of persons with special knowledge."

R. v. J.L.J. [Supreme Court of Canada] 2000
The Supreme Court expressly referenced Daubert as a relevant authority [FN2-19 below] where the Supreme Court expressly referenced Daubert as a relevant authority and referred to many of the same factors for analysis referenced by the Daubert court.  The Canadian law has now been made clear by the Supreme Court.

Bloodstain Related Case Rulings

R. v Luciano S.C.J. Jury No. 00/01161

Defense challenge-

1)  Witness did not pursue proper procedure in collecting and recording evidence.

2)  Witness lacked scientific training

3)  Witness is not impartial

Ruling: Witness was qualified to present expert evidence with respect to BPA



Strafprozessordnung Sto  Section 73 Selection of Experts



Coming Soon

Legal Discussion

Craig M. Cooley, Forensic Science and Capital Punishment Reform: An “Intellectually Honest” Assessment, 17 Geo. Mason U. Civ. Rts. L.J. 299 (2007).


Aaron D. Gopen and Edward J. Imwinkelried, Bloodstain Pattern Evidence Revisited, Criminal Law Bulletin, Volume 45, Issue 3 (Summer 2009).


Committee onIdentifying the Needs of the Forensic Sciences Community, National ResearchCouncil, Strengthening Forensic Science in the United States: A Path Forward,Doc. No. 228091 (August 2009)


Scientific Working Group on Bloodstain Pattern Analysis- Bibliography.