Bloodstain pattern analysis

Blood is an evidence found, and even sought, on scenes of violence.

Since 1985 and the work of Sir Alec Jeffreys, we have the opportunity to identify the source of blood through its DNA. If it is now possible to identify the blood, it remains crucial to identify the action that caused the deposition of this blood on the support studied, to be able to link it to the current investigation.

As soon as a blood vessel is injured, the blood moves out of the circulatory system according to the laws of physics. If a wound exists, the blood goes outside, and the bloodstains are created on the surrounding supports, according to various interactions of which the most common are:

• gravity (flow, …);

• the source-specific force exerting pressure on the liquid blood (cardiac pressure, exhalation, …);

• a force external to the source of blood (violent action, …);

• a force related to the movement of a bloody element (hand, hair, weapon, …);

• transfer by contact between two surfaces, at least one of which is bloody (transfer by contact, alteration by contact, transfer slipped, alteration slipped).

Named BLOODSTAIN PATTERN ANALYSIS this forensic Science determines the events at the origin of the stains studied. Whenever possible, it also establishes a chronology of these bloody events and locates the various actors (victim, aggressor, spectator …) during the determined bloodshed.

Thus, the study of the shapes, sizes, distributions and dispersions of bloodstains, provides information such as: the type of weapon used, the number of blows, the location of the aggressor and the victim when bloody projections, movements of people or bloody objects and the chronology of the bloody events.

This information is finally used to reconstruct the dynamics of the bloody events and if necessary, later compared to the statements of witnesses and suspects of these facts.

Previously, the medical examiner interpreted the bloodstains, alone, and without training, according to what he saw at the Crime Scene and during the autopsy (see the works mainly from US published from the second half of the 19th century, compiled by Herbert Leon MacDonell). Today, as a field of forensic science in its own right, the bloodstain pattern analysts must follow reproducible, objective and accredited methods to establish their conclusions.

To fulfill its mission, it is essential for the expert to study the documentation of the initial investigations. This first study can be supplemented by a study of the scene and the analysis of bloody clothing. This displacement is useful to better understand the volumes of the area, to check if all the bloodstains have been documented and the pictures of the initial investigations may not show all the edges characteristics use for the classification of the patterns of bloodstains and thus to answer the accurate questions concerning essentially the location of belligerents.

The presence of the Bloodstain Pattern Expert the reconstitution done by the magistrate can also be useful or even essential to verify the compatibility of the testimonies but also to facilitate the work of synthesis of the various expertise with the initial findings.

Philippe Esperança
Forensic Expert of the French Supreme Court
Bloodstain Pattern Analysis Expert of the Internation Criminal Court
IAI BPA Certification
Founder of the BPA sub WG of the European Network of Forensic Sciences Institutes (ENFSI)
International Association of Bloodstain pattern Analysts (IABPA) Vice President