Believe it or not, you can read blood spatter like a book. Hopefully, you will never be in a situation where you need to figure out a blood point of impact or how to read a blood-filled crime scene. Remember, you should not touch anything at a scene unless you are a law enforcement professional. However, if you understand blood spatter analysis, you can provide investigators with helpful insight when they make it to the scene.

The History of Blood Spatter Analysis

The science of “reading” blood spatter is called Blood Spatter Analysis. The concept began in 1895 when Dr. Eduard Piotrowski published a paper called “On the formation, form, direction, and spreading of blood stains after blunt trauma to the head.” The title of this paper sums up the taxonomy of blood spatter, after all, the point of studying the science is to deduce the how, what, where, and who of a crime scene. 

Dr. Piotrowski began experimenting on rabbits to study blood spatter further. It has been determined that pigs have the closest consistency to human blood, but Dr. Piotrowski was able to conduct helpful experiments to help understand blood spatter analysis. Many of his findings were published. However, he is only responsible for preliminary findings, not the exact analysis of science. For decades, investigators tried to get blood spatter analysis accepted in court. Finally, in 1957, the California Supreme Court was the first court in the United States to take science as hardcore evidence.

Why Read Blood?

We know it took several years for the justice system to recognize the validity of blood spatter analysis. But why was it such a struggle? Why is it so important to an investigation? One reason it may have been a challenge to get blood spatter analysis accepted is that though forensic science is a bona fide science, it is only one part of the evidence. 

An investigation requires physical or forensic evidence, witness statements, and more to seal the deal and solve a case. However, it is good that the court finally recognized blood spatter analysis as valid evidence. Blood spatter can provide information about how an incident occurred and in what order the events took place. Blood spatter analysis is extremely helpful for scenes with two conflicting stories or where there are no living witnesses.

For instance, if there is a non-fatal stabbing and one person is claiming the other person started the fight, blood spatter could help investigators determine who is telling the truth. Additionally, for a scene where there is a decedent who can no longer speak and there are no witnesses, blood spatter can help investigators determine where and how the struggle began.

It’s Importance

Blood spatter analysis has helped determine a suspect’s involvement and presence at a crime scene and the order and sequence of events. A case in 1978 was solved by an impact spatter on the suspect’s shoe. Garth MacDonald was found bludgeoned to death, and the only suspect was his boyfriend, Glenn Rycroft. Despite Rycroft stating the last time he saw MacDonald, he was safe and well, investigators noticed an impact spatter on his shoe. 

That particular type of blood stain could only appear if the person had been present during the crime. The impact spatter, as well as other evidence, led to Rycroft’s arrest for the murder of MacDonald. This case example shows that blood spatter analysis can prove what happened and where and can help sustain innocence or guilt.

Understanding blood spatter analysis requires a process, but once it is understood, the science is impactful and can help investigators solve cases.

Determining the Area of Impact

To determine what happened in a situation involving blood, you need to determine the origin of the impact, which is also known as the location of the event.

To determine the origin of impact, you take measurements of the blood stains and plug them into a trigonometry formula. Don’t worry, you don’t need to be a math whiz, it is pretty cut and dry. Remember the three main components: viscosity, surface tension, and density. Viscosity is the thickness of the fluid, surface tension refers to the energy needed for fluid to come into contact with a surface, and density refers to the mass per volume. Lost? Don’t worry, all will be revealed.

Patterns 

One of the other key points of understanding blood spatter analysis is understanding the patterns. Of course, every crime scene and every area containing blood will differ, but some common blood spatter patterns can help explain the events at hand. Some of the most common blood spatter patterns include blood pools, drops, swipes, wipes, pattern stains, and low, medium, and high-velocity spatter. 

By understanding a particular pattern, you can piece together the events when the incident occurred. Drops, in particular, can tell you what direction a blood source originated from. For example, not only should you pay attention to the direction where the blood drops are coming from, but you should also pay attention to the size of the drops themselves.

For example, if a blood drop is completely circular, it is a 90-degree drop that only occurs if someone or something with blood on them is standing still. The drip that occurs makes it a 90-degree angle.

The Devil is in the Details

When there is a slight “tail” on the end of the blood drop, that can also indicate direction.

If a large amount of blood is present, it can be challenging to pinpoint what happened at the time of the incident. However, with patience, small areas of blood may be focused on, which can provide insight into what occurred during the incident. Another aspect investigators look into is the blood’s appearance, meaning it is separated from other fluids or is still intact. 

When blood sits for more than 45 minutes, it separates, and areas start to dry or congeal. If blood has begun to separate, this indicates that the incident occurred at least 45 minutes earlier. This is extremely helpful for investigators when trying to coordinate witness statements and alibis. Just as the direction of blood spatter and the type of blood stain can determine a timeline of events, so can the condition of the blood itself.

Putting it All Together

You have various pieces of information, you have identified the blood stain patterns and which ones are most significant for determining what has occurred. Now what? It is now time to take every piece of information you have gathered and put it all together. Like any investigation element, all the pieces must be put together to solve the puzzle. Blood spatter analysis is one of the most puzzling sciences of all the forensic disciplines that exist. However, once each blood drop, pattern, and swipe are analyzed, the entire sequence of events may be put together.

Another aspect of analyzing blood spatter is noting when there is a void. What is a blood void pattern? A blood void is where there is a vacant area in blood, meaning that at the time of the incident, there was an object in that area, and it most likely has been removed, creating a void pattern. 

For example, if there is a pool of blood with a space shaped like a remote in the middle, we can assume there was a remote there at the time of the blood spill, and it has been removed. For those who are investigative professionals, blood void patterns are significant evidence that can reveal an important aspect of the story of what may have occurred. Often, what evidence isn’t present at the scene or what may be missing is just as significant as what is visible and present.

Here are the steps to analyzing blood spatter in order:

Step 1 – Note whether the blood is a stain or spatter. If the blood is considered to be spatter, then determine the specific types of patterns that are present.

Step 2 – Notate the direction of the blood. Ask yourself the following questions: Does the blood appear to be coming from a particular direction? Where is the largest area if it is a blood pool? Where does the blood drip taper off?

Step 3 – Note the size of the blood spatter, including both length and diameter. (DO NOT TOUCH IT!)

Step 4 – Take measurements and put them into the trigonometry formula.

The formula here: angle of impact = arcsin (stain width/stain length)

Step 5 – The angle will tell you where the incident began!

Take note of the condition of the blood as well, remember this may help determine the timeline of events as well.

Hopefully, you will never encounter blood spatter unless you are a professional and it is your job to investigate. But if you do encounter some, don’t touch anything. Call the cops, and maybe you can provide them with insight when they arrive to help solve a case.