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Bloodstain pattern analysis

Forensic method

  • 19 min read
  • 6 chapters

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Since the late 1950s, BPA experts have claimed to be able to use biology, physics, and mathematical calculations to reconstruct with accuracy events at a crime scene, and these claims have been accepted by the criminal justice system in the US. Bloodstain pattern analysts use a variety of different classification methods. The most common classification method was created by S. James, P. Kish, and P. Sutton, and it divides bloodstains into three categories: passive, spatter, and altered.

Despite its importance, classifying bloodstain patterns poses challenges due to the absence of a universally accepted methodology and the natural uncertainty in interpreting such patterns. Current classification methods often describe pattern types based on their formation mechanisms rather than observable characteristics, complicating the analysis process. Ideally, BPA involves meticulous evaluation of pattern characteristics against objective criteria, followed by interpretation to aid crime scene reconstruction. However, the lack of discipline standards in methodology underscores the need for consistency and rigor in BPA practices.

The validity of bloodstain pattern analysis has been questioned since the 1990s, and more recent studies cast significant doubt on its accuracy. A comprehensive 2009 National Academy of Sciences report concluded that "the uncertainties associated with bloodstain pattern analysis are enormous" and that purported bloodstain pattern experts' opinions are "more subjective than scientific". The report highlighted several incidents of blood spatter analysts overstating their qualifications and questioned the reliability of their methods. In 2021, the largest-to-date study on the accuracy of BPA was published, with results "show[ing] that [BPA conclusions] were often erroneous and often contradicted other analysts."

History

Early history

Bloodstain pattern analysis has been used informally for centuries, but the first modern study of blood stains was in 1895. Dr. Eduard Piotrowski of the University of Kraków published a paper titled "On the formation, form, direction, and spreading of blood stains after blunt trauma to the head." He conducted his first experiments on rabbits. A number of publications describing various aspects of blood stains were published, but his publication did not lead to a systematic analysis. LeMoyne Snyder's widely used book Homicide Investigation (first published in 1941 and updated occasionally through at least the 1970s) also briefly mentioned details that later bloodstain experts would expand upon (e.g., that blood dries at a relatively predictable rate; that arterial blood is a brighter red color than other blood; that bloodstains tend to fall in certain patterns based on the motion of an attacker and victim). A 1952 episode of the police procedural radio series Dragnet made reference to bloodstain pattern analysis to reconstruct a shooting incident.

Acceptance as valid evidence in United States courts

Between 1880 and 1957, courts in Michigan, Mississippi, Ohio, and California rejected expert testimony for bloodspatter analysis, generally holding that it added nothing to the jurors' own evaluations of bloodstains submitted as evidence. In 1957, the California Supreme Court became the first American court to accept expert testimony examining bloodstains, accepting as evidence the testimony of Paul L. Kirk, a professor of biochemistry and criminalistics. He would also testify in the Sam Sheppard case in 1966, when the wife of an osteopathic physician was beaten to death in her home, interpreting bloodspatter evidence as proof that the murderer was left-handed (Sheppard was right-handed). However, bloodstain pattern analysis would not begin to enter wide use until it was promoted by Herbert Leon MacDonell. MacDonell researched bloodstains with a grant from the United States Department of Justice, and which also published his research in the book "Flight Characteristics and Stain Patterns of Human Blood" (1971). The basis for MacDonell's alleged expertise was a set of experiments he conducted by extracting his own blood and then slinging it around in the basement of his house in Corning, New York. MacDonell testified in court on multiple occasions as an expert of bloodstain analysis, and the legal precedent set by these cases led to its widespread use in American courts, although as early as 1980 some judges expressed strong doubts about its reliability, and it was not always accepted as evidence, especially in states with no prior rulings that relied on such evidence.

The first formal bloodstain training course was given by MacDonell in 1973 in Jackson, Mississippi. MacDonell taught workshops on how to conduct bloodstain analysis, and the newly trained bloodstain analysts, who often had received as little as 40 hours of instruction, in turn would give expert testimony in court cases. In 1983, the International Association of Bloodstain Pattern Analysts was founded by a group of blood stain analysts to help develop the emerging field of bloodstain pattern analysis.

Further investigation into its admissibility as evidence

Starting in 1995, court cases where bloodstain analysts disagreed with each other raised concerns of the discipline's prediction's admissibility as evidence in court. In 2009, the National Academy of Sciences published an examination of forensic methods used in United States courts which harshly criticized both bloodstain pattern analysis and the credentials of the majority of the analysts and experts in the field. Judges have largely ignored the report's findings and continue to accept bloodstain pattern analysis as expert evidence.

In 2013 Daniel Attinger, a fluid dynamics researcher at Columbia University, published a paper on bloodstain pattern analysis in Forensic Science International, finding that many of the central hypotheses of bloodstain analysis remain untested, and that existing analysts often made incorrect assumptions or other errors in their analyses. The paper also proposed fluid dynamics as a theoretical framework for solving these problems, and Attinger has continued to publish several papers exploring these concepts (as have other scientists as well). However, these papers are largely theoretical, and have had little impact on the use of bloodstain analysis in courts.

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