Burgess, R. L. (2023). Bloodstain Pattern Analysis (BPA). QFSA.

Bloodstain Pattern Analysis (BPA)

Blood (commonly called “splatter) Analysis (BPA) involves reconstructing events that happened during a crime that resulted in a bleeding injury. Two types of blood pattern reconstruction exist, both require a BPA specialist to conduct:

1. Scene Pattern Reconstruction: which involvedetermination ofstain condition, pattern, distribution, location, and directionality

2. Lab Results Reconstruction: which involvewhich involvegenetic marker typingand thedetermination of age, source, race, and sex.

Bloodstain Types:

1. Passive Stains:drops, flows, and pools.

Passive stains typically form after blood droplets fall towards a surface at a 90° angle, producing circular droplets if the surface is smooth or secondary satellites it is a textured surface. Pools form around victims who are bleeding heavily are that remain in one location. If the victim was moved, blood droplets connecting one location to the next may occur. These are called "drip trails" are another type of pattern in this category and are caused by depositing of blood from the victim as they move locations, appearing as either round, smeared, or spurts(GFJC, 2013; Freeman & McManus, 2022).

2. Transfer Stains:wipes, swipes, and pattern transfers.

These are left when a victim is bleeding and blood becomes deposited through touching or brushing against objects (i.e., a walls, furniture, etc.) which the blood transfers onto that object(s). Wipe patterns are result from objects moving through a bloodstain, compared to swipe patterns that result from objects leaving a bloodstain.

3. Projected and Impact Stains:Arterial spurts and gushes, splashes, and mists.

Arterial spurts and gushes usually can be located on either walls or ceilings and caused from the heart's pumping action.Another type of pattern, calledsplashes, have a noticeable "exclamation point" shape. The shape and position of this pattern helps locate the victim's position at the time of the injury.Lastly, mists are a pattern caused by incidents involving high velocityblood spatter, such as suicide bombings and explosions.

What impacts the shape of blood droplets?

1. Size (blood spatter): Blood spatter from a high-velocity incident like a suicide bombing will create a cast-off pattern much different from a lower-velocity pattern like a gunshot or stabbing. Blood spatters help recreate crimes at the time they happened using basic concepts like the laws of motion, gravity, physics, and chemistry. Blood travels in spherical drops due to surface tension, defined as a liquid's tendency to minimize surface area resulting from molecule attraction to each other (i.e., it's cohesive). Droplets also have predictable patterns of behaviour when they strike surfaces or when being acted on by an outside force.

2. Velocity: The speed blood droplets travel (in a spherical fashion) when they strike a surface (i.e., the target) has an impact on the shape of the blood droplet, in combination with angle and surface characteristics, which will determine the distance that blood droplets can skip or bounce after meeting a barrier.

·       Examples of low velocity blood spatter sources(5 f/s, 1.5 m/s): bloody noses, weapons/objects that are motionless and covered in blood.

·       Examples of medium velocity spatter sources (Between 25 to 100f/s, 7.5-30m/s): blunt objects, stabbings, or coughs containing blood.

·       Examples of high velocity blood spatter sources (>100f/s, 30 m/s): gunshot wounds, explosions, power tools or high-speed machinery. Bloodstains in this category will typically measure less than 0.04 inches/1 mm across.

3. Height: Blood droplet diameter increases proportionally to the height it falls from (Freeman & McManus, 2022).

4. Surface Texture: If the surface texture is flat (i.e., glass or marble), the blood droplet edges will appear smooth and circular. However, if the surface texture is porous, the edges of the blood droplets edges may form small spikes (extensions) or satellites. Importantly, spinesare attached to main droplet whereas satellitesare not attached to parent droplet (center of blood droplet).

Blood Droplet Shapes & Angle of Impact (AOI)

Blood droplet shape matters - the more acute the AOI = the increased elongation of bloodstain.

Perfectly round blood droplets are indicated by falling onto target surfaces from 90° angles. Meanwhile, elliptical blood droplets are measured at 80° because they're  slightly elongated as their angle decreases from 90°-0°. Generally, the tail on a blood droplet begins production at ~30°, with the more acute angles being easier for experts to determine the direction of travel. The following formula, known as the Impact Angle Formula, is used:

angle of impact = arcsine (stain width / stain length)

Determining the Area of Convergence and Point of Origin

The point of convergence is known as the common point or area on a 2D surface where the directionality of multiple blood droplets are retraceable. The point of origin is the common point or area inside a 3D space to which the trajectories of multiple blood droplets are retraceable. The original source location can be determined by drawing lines using multiple droplets and finding a singular point each of them intersect (Freeman & McManus, 2022).

References

Freeman, S., & McManus, M. R. (2022). How bloodstain pattern analysis works. HowStuffWorks. https://science.howstuffworks.com/bloodstain-pattern-analysis3.htm

Global Forensic and Justice Center (GFJC). (2013). Bloodstain pattern analysis: How it’s done. (2013). https://www.forensicsciencesimplified.org/blood/how.html

Lee, H. C., & O'Neil, T. W. (2011). Cracking cases: The science of solving crimes. Prometheus Books.

Rosina, J., Kvasnak, E., Suta, D., Kolarova, H., Malek, J., & Krajci, L. (2007). Temperature dependence of blood surface tension. Physiological Research, 56(1), S93.