Bloodstain Pattern Analysis and Its Problematic Role in Forensic Science

Bloodstain Pattern Analysis and Its Problematic Role in Forensic Science

This article relates to The Good Liar

The protagonist of The Good Liar is a forensic scientist who has developed the Blood Spatter Probability Scale (BSPS), a fictional modeling system that uses blood spatter information from a crime scene to create a 3D model reconstruction of the events. Although bloodstain pattern analysis has been used to help solve real crimes for over a century, recent studies have discovered that many factors can influence the analysis of bloodstain patterns and create inconsistencies that could result in false convictions, as happens with the BSPS in The Good Liar.

Bloodstain pattern (BSP) analysis is the examination of the location, size, shape, and distribution of bloodstains at a crime scene. When these factors are analyzed in the context of known forces, such as gravity, acting upon drops of blood, the results can provide information regarding the event(s) that created the pattern. Analyzing BSPs is not as simple as it may seem; experts in BSP analysis must receive formal education and training in the field and typically have at least several years of experience before they are considered an expert witness in a court of law. The best analysts must have significant understanding of the various forces that can affect blood once it leaves the body, including applied mathematics and the physics of fluid transfer, as well as the pathology of wounds and the limitations of the various tools used in the analysis of the BSPs.

Recent studies, including an investigation by the United States National Academy of Sciences, have found that most forensic methods, including BSP analysis, have some degree of subjectivity, which impacts the use of these methods in determining the nature of crimes. In fact, when asked to analyze a set of BSPs, it was found that different experts frequently came to different conclusions about the source of the BSP, and even the same expert came to different conclusions upon repeat examination of the same case. This subjectivity may be influenced by personal biases as well as biases created by contextual information surrounding the case, such as the presence of weapons at the scene or police theories. These factors may unconsciously cause analysts to read the BSPs in a way that fits what the police have proposed, whether or not that's the most accurate analysis of the data.

The question has also been posed as to whether BSP analysis can even theoretically provide an accurate assessment of the data, let alone practically. There are countless variables that can impact the BSP after an event: environmental factors, contaminants (dust, fingerprint residue, paint) on surfaces, the size and shape of the weapon, the presence of anti-coagulants in the victim's bloodstream, the absorbency of the clothing, the angle of impact, the blood vessels hit, and more. Although BSP analysis is based on sound scientific principles and proven natural forces, there is such a wide variety of factors that can impact even the baseline data of a BSP that many argue that the methodology is not theoretically valid.

What can be done to increase the validity of BSP analysis and make it a less subjective method for helping solve crimes? At Boston University, researchers in fluid mechanics are currently working on projects that would help eliminate at least some of the variables impacting the theoretical validity of BSP analysis. Dr. James Bird at the College of Engineering is researching the characteristics of blood evidence under crime scene conditions (for example, dirty surfaces), as well as how fluids like blood act on hydrophobic surfaces (cell phone screens, waxed floors), to help prove that blood reacts in a unique way depending on the sometimes-invisible coatings found on surfaces. Other researchers are developing a real version of the BSPS, incorporating 3D modeling and virtual reality simulations to help show the spatial relationships between BSPs and other elements of the crime scene and to reconstruct the inciting event in conjunction with other evidence. Although this current research is hoping to decrease subjectivity and variables, the current status of BSP analysis is still problematic as a forensic method.

Image of blood spatter by jimmy brown, CC BY 2.0.

Filed under Medicine, Science and Tech

This article relates to The Good Liar. It first ran in the September 10, 2025 issue of BookBrowse Recommends.