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Bloodstain Pattern Analysis

Bloodstain pattern analysis involves the study of the static consequences (blood splatters) resulting from blood shedding. The analysis focuses on factors such as distribution, size and shape of bloodstains, and location of the spatter. These components, when correctly analyzed, can help reconstruct the event that led to the bloodstain. Bloodstain pattern analysis (BPA) can also help validate or disprove statements provided by suspects, victims, or witnesses.


How it Works

Blood is like every other object on Earth in that its behavior conforms to the laws of physics. Bloodstain pattern analyzers have a very thorough understanding of physics. While blood has many physical properties that are similar to the properties of water, blood responds differently to the same external forces because blood has a different viscosity, adhesion, capillary action, and density. These factors, after examined in a laboratory, can be translated to crime scenes. In the physical location, it is important to note the surface the blood landed on, whether it is smooth or rough, porous or teflon. These factors are referred to as surface tension. Bloodstain pattern analysis teaches us facts like these, which can be used to determine the events that led to the blood stain:

Blood striking an object at angles less than 90 degrees produces a tear drop shape. A 90-degree impact angle will yield a circular shape.

When blood forcefully strikes a surface at sharp angles, a smaller droplet is cast-off from the larger parent drop.

The movement and the number of swings during a beating with an instrument can often be determined by examining the blood droplets that are cast-off the surface of the instrument.


How to become a Bloodstain Pattern Analyst

Like many forensic science technicians, bloodstain pattern analysts often require strong backgrounds in scientific studies, like one of the natural sciences. Bachelor’s degrees are often mandatory. Criminology and criminal justice associate’s degrees are sometimes acceptable, but not preferred, as blood splatter experts deal with additional academic areas, such as chemistry, mathematics, and physics.

In addition to a bachelor’s degree, bloodstain pattern analysts are also required to undergo special training as set out by the International Association for Identification. The International Association for Identification has laid out a specific set of requirements before they will grant certification, including a minimum of forty hours of education in an approved workshop, a minimum of three years of practice within the discipline of bloodstain Pattern Identification, and a 75% or higher on their written examination. Furthermore, other advanced training and courses are also available, and often recommended as analysts become established in their careers.


Further Reading

Indiana State Police Bloodstain Pattern Analysis Test Methods – From Indiana’s finest, the manual for bloodstain pattern analyzers, including a helpful appendix of crime scene protocol.

Bloodstain Pattern Analysis Video Collection – From the U.S. Department of Energy comes an impressive assortment of bloodletting mechanism video clips.

Blood Overview – A thorough collection of slides reviewing the basic and not-so basic attributes of blood in the body, including a detailed look at the composition of blood.

How Bloodstain Pattern Analysis Works – A great infographic from the Discovery Channel, explaining types of spatters, what BPA can determine, and how to analyze the path of the blood drop and calculate the impact angle.

Introduction to Bloodstain Pattern Analysis – An excerpt from Penn State University’s online forensic science course, this book chapter available in pdf format includes a look at different historical perspective of BPA, common terminology, and addresses the scientific basis for BPA.

International Association of Bloodstain Pattern Analysis – This organization has free pdf’s of their self-published Journal of Bloodstain Pattern Analysis available for non-members. Each issue has several articles and images regarding studies, new techniques in BPA, and more.

Strengthening Forensic Science in the United States: A Path Forward – Available for free online, this book examines the need to encourage congress and policy makers to better fund forensic science and provides great information necessary for law enforcement agencies, criminal prosecutors and attorneys, and forensic science educators.


*images courtesy of Wikimedia commons