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The results will generally take the form of a technical report that outlines the findings of the analyst. BPA results will generally include, in the opinion of the analyst, the following information for each stain or pattern found at the scene:
- How the bloodstains were formed (type of instrument and action that caused the stains)
- Number of victims (confirms case information)
- When possible, the approximate number of perpetrators
- The approximate position of the victim(s) (standing, sitting, lying on the floor, etc.) using area of convergence and origin
- When possible, the relative position(s) of the victim(s) to the perpetrator(s)
Photographs and diagrams may accompany the report to provide additional details about the scene.
Limitations of the BPA include the fact that it cannot recreate the entire scenario, as there are unknown variables that analysts cannot account for using scientific methods. For example, the analyst cannot tell if a perpetrator was older or younger, if an attack was planned or spontaneous, or if drugs or alcohol influenced the perpetrator (unless their blood was left behind). BPA recreates the actions of specific blood shedding events with reasonable certainty based on measurements and understanding of the scientifically understood behavior of blood, not supposition or inference. The results of bloodstain pattern analysis are often used to support or confirm the findings of other forensic disciplines used in the case.
To ensure the most accurate analysis of evidence, the management of forensic laboratories puts in place policies and procedures that govern facilities and equipment, methods and procedures, and analyst qualifications and training. Depending on the state in which it operates, a crime laboratory may be required to achieve accreditation to verify that it meets quality standards. There are two internationally recognized accrediting programs in the U.S. focused on forensic laboratories: The American Society of Crime Laboratory Directors Laboratory Accreditation Board and ANSI-ASQ National Accreditation Board / FQS.
In bloodstain pattern analysis, quality control is achieved through proper training and competency testing for analysts, as well as technical review and verification of conclusions. Technical review and verification involves an expert or peer who reviews the data, methodology and results to validate or refute the outcome. This review encompasses the analysis and observations, laboratory work, tests and experiments, bench notes and written reports. The percentage of cases that undergo verification may vary depending on the experience of the analyst. In addition, defense attorneys may hire independent BPA analysts to review and reexamine questioned evidence to ensure accuracy of the findings.
SWGSTAIN publishes Guidelines for a Quality Assurance Program in Bloodstain Pattern Analysis on their website.
Reports will vary from jurisdiction to jurisdiction; however, SWGSTAIN maintains recommended standard operating procedures for final reports. According to these guidelines, reports should ideally contain:
- Items of evidence or materials evaluated (usually photographs or diagrams and other reports)
- Observations and results of the analysis
- Conclusions and opinions of the analyst
- Definitions of terminology used in the report
- Brief summary of the case
- Description and results of any experiments conducted
Conclusions and opinions of the analyst typically include information about how the stains were formed and the approximate position of the victim (standing, sitting, lying on the floor, etc.). Photographs and diagrams included in the report serve to illustrate the location and pattern of the stains and, where known, the relative positions of the victim and perpetrator.
In most cases, the analyst will be prepared to testify in court regarding the results.
Are there any misconceptions or anything else about bloodstain pattern analysis that would be important to the non-scientist?
Bloodstain pattern analysis is not a recent field of study; it has been around since the late 1800s. In 1895, Dr. Eduard Piotrowski of the Institute of Forensic Medicine in Krakow, Poland, published a paper on bloodstain pattern analysis titled Concerning Origin, Shape, Direction and Distribution of Bloodstains following Head Wounds Caused by Blows. Dr. Piotrowski performed experiments using live rabbits, white paper and a variety of instruments including rocks, hammers and hatchets to better understand how bloodstains are created and what information could be gleaned from their study.
Misconception: Blood spatter tells the whole story
Television crime dramas paint bloodstain analysts as being able to tell investigators everything that occurred at a crime scene based solely on a few blood splashes or spatters. This is far from the truth. As discussed earlier, BPA cannot produce a playback of the entire crime. Bloodstains tell analysts, with reasonable certainty, what happened at specific moments in time corresponding to each useable stain. In some cases, the bloodstains are too few or the volume of blood is too great for analysts to reasonably render any opinion on the causes of the stains.