Interpreting Blood Spatter Evidence

When thinking of things that should be up to interpretation, we think of art, such as paintings, poems, movies, and so forth. There are even laws that can be interpreted differently.

However, when it comes to proving criminal activity, one would hope it is primarily fact-based. So it's alarming when interpretation plays a significant role in how evidence is assessed.

After all, someone's freedom, reputation, and familial relationships shouldn't be left to interpretation. But some types of evidence, such as blood spatter evidence, don't necessarily lend themselves to objective, ironclad conclusions, as one would hope.

In fact, you'll find that different conclusions can be drawn from the same evidence, as we examine the findings of the following articles: Louis L. Akin. Interpretation of Blood Spatter for Defense Attorneys—Part I. The Champion (NACDL), April 2005 p. 38-41 & Part II. The Champion (NACDL), May 2005 p. 26-29.

We mentioned various art forms in the introduction to juxtapose them with something we assume to be science: analyzing evidence.

However, when evidence is assessed and examined, it is just as much an art form as any Van Gogh painting. It's not hard science.

For defense attorneys, this factor can play a massive role in proving our clients' innocence. Of course, this necessitates that we have a firm grasp over the principles and procedures of blood spatter analysis.

These principles and procedures include factors such as:

• The positions of victim, assailant, and objects at the scene
• The type of weapon used that led to the spatter
• The sequence of events
• Who was there at the time of the alleged criminal act

We are only scratching the surface here, but this is just to give you an idea of what we need to know as attorneys.

Let us assess one example of blood spatter that can lead to confusion and different conclusions—that being arterial blood spatter.

Arterial blood spurts can be characterized as follows:

• It displays itself in squirted arcs due to pumping from the left ventricle of the heart.
• During ventricle contractions, blood squirts excessively from the artery.
• The squirting's change in intensity causes an arcing pulse that results in a distinctive blood pattern.

Arterial blood often gets confused with cast-off blood patterns. Or it can be clouded by layover patterns. A victim could still be under attack while arterially bleeding and sustaining further wounds or blood might be pouring from previous injuries.

Bloody handprints, swipe/wipe, and other transfer blood usually accompany arcs. Also, the victims might smear the pattern because they fall against the spatter. They could also spread blood from their body or clothing onto the surface.

This explanation makes it evident that weapon cast-off could generate multiple interpretations of the same blood spatter.

Other factors the convolute blood spatter analysis are various angles, velocity, weapon cast-off, and many more.

None of these assessment tools are exact and rely on interpretation of the facts.

Blood spatter analysis procedures are similar to a tracker reading a trail sign. While we'd prefer it was more like a hematologist working in a lab with a purely objective viewpoint, this is far from the case.

Analysts are given other evidence, autopsy reports, police reports, and witness statements. Plus, these forensic professionals have their own notions about the scene. They're also aware of different dynamics, such as ballistics and wounds to the human body.

These factors play a role in how these specialists interpret the blood patterns present at the crime scene, potentially leading to biases and filling in gaps according to other evidence.

Instead of making proclamations of precisely what happened, these specialists tell you what they believe has occurred. As such, it should not be a surprise that different blood spatter examiners could have contrasting interpretations.

Interestingly, even with these factors in mind, blood spatter analysis has been accepted throughout the U.S. as reliable evidence.

Blood spatter analysis is a complicated, and some would say unproven, forensic science practice. There are stories where analysts with minimal training have been integral in successful prosecutions, with little being done to rectify those situations.

If such evidence is being presented as evidence in the case against you, you need to have a defense team capable of thoroughly analyzing the evidence and critiquing the interpretation of that evidence. You may need a second opinion from another forensic expert to discredit the government’s analysis.