# Forensics and Computer Vision: Blood Spatter Analysis

November 21, 2017

Often found at the scenes of violent crimes, the analysis of bloodstains can provide vital clues as to the occurrence of events Bloodstain Pattern Analysis is a forensic discipline in which, among others, the position of victims can be determined at crime scenes on which blood has been shed. Therefore, we studied in details about blood spatter analysis and their pattern analysis in image processing system.

### Blood Spatter Analysis : Significance

Some scenes of violent crime contain blood stains. Blood spatter stains occur when blood falls passively due to force being applied to a body. There is a well established though extremely tedious technique by which a specially trained forensic technician can analyze the individual blood spots. Blood spatter analysis is performed by forensics experts at crime scenes where impact on a body has caused blood to fly off and land on surrounding surfaces. The resulting stains are affected by many physical variables, such as speed, liquid density, and the material properties of the surface. However, the shape of the stains, in this case the spatter pattern, does reveal information that can be useful to investigators. Subsequent developments have led to the emergence of Blood Spatter Analysis as a forensic specialization.

### Blood Spatter Analysis : Definition

A blood-spatter pattern is a collection of bloodstains produced by drops of blood that have traveled through the air, from a source location to a target surface. One of the main issues in forensic analysis of blood-spatter patterns is to determine where a blood spatter originates from. This serves the purpose in crime scene reconstruction of determining the position of the source of blood. This type of knowledge is expected by the analyst communities [21] as it provides a deeper understanding of what occurred during the crime. The position of the source of blood is typically obtained by backward reconstruction of the trajectories, from the target to the source. A sound fluid-mechanical theory of drop atomization, trajectories, and impact would be relevant to the interpretation of blood spatters resulting from gunshot wounds such as the infamous case of Phil Spector, where the question arose of if blood from the back spatter could travel a distance of approximately 1.8 m.

Blood splatter analysis is a huge part of any forensic analytics, which deals with crime scene investigations, which are in need of reconstruction of the crime scene in order to get a deeper look and insights into the crime scene itself and find out more details towards solving the crime

### Bloodstain Pattern Analysis

Bloodstain Pattern Analysis (BPA) is defined as the study of the shapes, sizes, distribution and locations of bloodstains in order to determine the physical events which gave rise to their origin. Bloodstain pattern analysis (BPA) is a subspecialty of forensic sciences, dealing with the analysis and interpretation of bloodstains found on a crime scene. A typical goal of a pattern analyst is to approximate the flight paths of several stains by estimating their impact and glancing angle, and subsequently estimate their area of origin through directional analysis.

BPA provides information not only about what happened, but just as importantly, what could not have happened. This information can assist the investigator in reconstructing the crime, corroborating statements from witnesses, and including or excluding potential perpetrators from the investigation.

### Principles of Bloodstain Pattern Analysis

To understand how analysts interpret bloodstains, one must first understand the basic properties of blood. Blood contains both liquid (plasma and serum) and solids (red blood cells, white blood cells, platelets and proteins). Blood is in a liquid state when inside the body, and when it exits the body, it does so as a liquid. But as anyone who has had a cut or a scrape knows, it doesn’t remain a liquid for long. Except for people with hemophilia, blood will begin to clot within a few minutes, forming a dark, shiny gel-like substance that grows more solid as time progresses. The presence of blood clots in bloodstains can indicate that the attack was prolonged, or that the victim was bleeding for some time after the injury occurred .

Blood can leave the body in many different ways, depending on the type of injury inflicted. It can flow, drip, spray, spurt, gush or just ooze from wounds.

### Types of Stains

Bloodstains are classified into three basic types: passive stains, transfer stains and projected or impact stains. Passive stains include drops, flow and pools, and typically result from gravity acting on an injured body. Transfer stains result from objects coming into contact with existing bloodstains and leaving wipes, swipes or pattern transfers behind such as a bloody shoe print or a smear from a body being dragged. Impact stains result from blood projecting through the air and are usually seen as spatter, but may also include gushes, splashes and arterial spurts.

Blood spatter is categorized as impact spatter (created when a force is applied to a liquid blood source) or projection spatter (caused by arterial spurting, expirated spray or spatter cast off an object). The characteristics of blood spatter depend on the speed at which the blood leaves the body and the type of force applied to the blood source.

Figure 1 Passive bloodstain on a wooden floorboard

Figure 2 Transfer pattern made by a bloody hand

Figure 3: Transfer pattern made by a bloody hand

### References

[1] W. G. Eckert and S. H. James, “Interpretation of Bloodstain Evidence at Crime Scenes”, Elsevier Publishing Company, 1989

[2] S. Weidman, Strengthening forensic science in the United States: A path forward, Committee on Identifying the Needs of the Forensic Sciences Community, National Research Council, 2009,

[3] Comiskey, P. M., “Prediction of blood back spatter from a gunshot in bloodstain pattern analysis”, Physical Review Fluids 1.4 (2016)

[4] Carter, A. L. “The directional analysis of bloodstain patterns theory and experimental validation.” Canadian Society of Forensic Science Journal 34.4 (2001): pp. 173-189.

[5] Brodbeck Silke, “Introduction to Bloodstain Pattern Analysis”, .SIAK-Journal – Journal for Police Science and Practice, Volume 2, pp. 51-57, 2012

• Xavier Billingsley November 22, 2017 at 1:07 am

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