Blood Spatter Analysis

What Is Blood Spatter Analysis?

To make an analyst in blood interpretation, one must first understand the basic concepts of blood. Blood is made up of two liquids, plasma and serum, and other solids such as red blood cells, white blood cells, platelets, and proteins. When in the body, blood is usually in liquid form and it remains so even when it exits.

However, as we can all bear witness, blood from a cut or clot will not stay in liquid for long. Except for people suffering from hemophilia where the blood will begin to clot forming a dark, shiny gel-like substance that gradually solidifies.

The presence of blood clots in bloodstains is an indicator of a possible struggle or attack that was prolonged, or where the victim was injured and still bleeding long after they had been wounded.

Blood can exit from the body in different ways depending on what has inflicted the injury. It can either spray, gush, flow, drip, or just ooze from the wounds.

Types Of Stains

Passive bloodstain Bloody shoe transfer pattern

There are three broad categories: transfer strains, passive strains, and projected or impact strains.

Transfer strains

Transfer strains result by coming into contact with existing bloodstains and leaving swipes, wipes, or patterns of transfer such smears of blood on walls or bloody shoe trails.

Passive strains

It include flows, drops and pools of blood typically resulting from gravity action on the injured part of the victim.

Finally, impact strains are strains that result from aerial projections usually identified as spatters but may also include splashes, gushes, and arterial spurts.

Blood spatter

It is categorized as either an impact strain because it is created upon exertion of a force on a liquid blood source or a projection spatter that was made through expirated spray, arterial spurting or cast off an object.

The characteristics of the blood spatter depends on the force applied to the blood source and the speed at which blood exits the body.

Gunshot spatter

It includes both the forward and back spatters for the exit and entrance wounds respectively. Spatters from a gunshot will vary depending on the type of the gun, the region that is hit, whether the bulhe body.

distance between the victim and the shooter, and the position of the victim with respect to floors, walls and objects. Notably, forward spatter is characterized by fine mist whereas back spatter is identified by larger and fewer drops.

Cast-off

It results when an object attached to an arc flings blood onto the surrounding surface. This mainly happens when the assailant throws the object in air before inflicting another blow. Analysts are able to tell the direction of the weapon used by the shape of the spatter. Recording the arcs can also assist in identifying the number of blows delivered.

Arterial spray

It refers to the major spurt of blood that occurs when an artery blood vessel is critically injured. The blood is pushed out of the wounded vessel by the rapid pumping of the heart. The spurt blood forms an arcing pattern containing large, individual stains, with a new pattern generated after each heart-beat.

Expirated spatter

It is usually as a result of an internal injury mixing with air that is expressly from the lungs and is expelled through the mouth, nose, and an injury to the airways or the lungs. Spatters formed by expirated spatter are fine and mist due to pressure exerted by the lungs during exhalation. Small bubbles are more often than not found in such a spatter.

Some bloodstains cannot be viewed with a naked eye and therefore require expert use of reagents such as luminol to identify and photograph latent bloodstains. When immersed in blood, luminol forms a luminescent glow by reacting with iron element present in blood’s hemoglobin.

Bloodshed Events

A crime scene where injuries are surmountable, evidence in form of bloodstains is present. However, the amount available will depend on the circumstance of the violent crime. The type of injury inflicted to the victim and the force applied will be explained by the volume and pattern of the bloodstain:

• Stabbing or sharp force injuries: these are often caused by sharp objects which have a relatively small surface are such as a knife, or an ice pick. Less blood is left on the objects, making smaller and more linear strain patterns.
• Blunt force injuries (beating or hitting): objects causing such injuries are usually larger and may include a hammer or a bat. If the large object impacts on liquid blood, the large surface area will remain with more blood that produces drops of different sizes.
• Gunshot injuries: mist-like spatters caused by bullets entering or exiting the body.

Interpreting The Patterns

Left: A large volume of blood Right: Impact spatter pattern

When blood is impacted, droplets are sent in all directions through the air. When these droplets land onto a surface, they form varying shapes depending on the angle of impact, distance travelled, velocity and type of surface impacted. Generally, the stains will take a circular or elliptical shape with spines or tails following in the direction of travel.

Smaller stains may also dissociate from the initial drop. By determining the dimensions of the stain, the angle of impact can be attained, helping investigators to create a vivid picture of what has taken place at the crime scene. As the angle shifts so do the appearance of the stain.

A blood drop impacting at an angle of 90° will result in an almost circular strain with less elongation and even distribution of the spines outside the drop.

Below 75°, the spatter elongates and becomes more elliptical as the spines and tails become more predominant on the opposite angle of impact. At extremely lower angles, the satellite may break off to create a secondary strain that is distinctive otherwise, the “exclamation point”

Void Patterns

A void pattern occurs when a blood path is disrupted by a person or an object. This analysis is important to analysts as they can identify whether certain persons or objects are missing from a scene or not.

It can track the person’s whereabouts during the time of the incident as well as determine if a body has been moved. An object that leaves a void in a blood spatter pattern will contain a matching pattern on its surface.

This allows analysts to replace it in the scene where it was initially. Void pattern analysis has proven useful in forensic investigations and in establishing the positions of both the assailant and the victim within a scene.

References

1. Bevel, Tom, and Gardner, Ross M. Blood Pattern Analysis, Second Edition. CRC Press, Boca Raton, FL (2002).
2. James, Stuart H., Kish, Paul E., and Sutton, T. Paulette. Principles of Bloodstain Pattern Analysis: Theory and Practice, CRC Press, Boca Raton, FL (2005).
3. James, Stuart H., Kish, Paul E., and Sutton, T. Paulette. “Chapter 12: Recognition of Bloodstain Patterns,” Forensic Science: An Introduction to Scientific and Investigative Techniques, CRC Press, Boca Raton, FL (2009), pp. 211–239.
4. Lyle, D.P., M.D. “Chapter 9: Serology: Blood and Other Body Fluids,” Forensics: A Guide for Writers (Howdunit), Writer’s Digest Books, Cincinnati, OH (2008), pp. 176–196.
5. Lyle, D.P., M.D. “Chapter 13: Bloodstains: Patterns Tell the Story,” Forensics: A Guide for Writers (Howdunit), Writer’s Digest Books, Cincinnati, OH (2008), pp. 285–302.
6. Saferstein, Richard. Forensic Science: From the Crime Scene to the Crime Lab, Pearson Education, Inc., Upper Saddle River, NJ (2009).