Blood Spatter Forensics: How It Can Help Solve Crimes
Understanding blood spatters as evidence
If you turn on your TV at night, there is a good chance that you will come across a TV show where investigators are using some sort of forensic or scientific method to collect or identify evidence. If you don’t like TV crime shows, you can turn to the actual TV shows where they break down a crime scene that has already been solved and the suspect is convicted using forensic evidence collected at the scene.
With over thirty years of police investigative experience working on hundreds of homicide cases, I can assure you today; if you take a case in front of a jury, you better be able to produce some sort of forensic or scientific evidence if you want a conviction.
In this article I will explain some of the basics of blood evidence and how to interpret the clues that blood evidence leaves behind.
Blood patterns and the interpretation of bloodstain patterns are very compelling evidence when used by an investigator who understands and can identify and explain them.
Blood evidence is most commonly used by police investigators in criminal cases who have experience and training in blood spatter. However, if a private investigator is assisting in a defense case with a lawyer or working with a family on a wrongful death case and he/she has an understanding and knowledge of blood patterns, he/she can be just as helpful.
Some of the things that blood evidence can show are movement and momentum during an attack, the type of weapon, and whether more than one type of weapon was used. It will reveal to the trained eye how many times the weapon or weapons were used, and the distance between the victim and the attacker.
There are three basic types of blood patterns:
(1) Splash at low speed.
This occurs with a minimal amount or no force. The blood pattern is much larger than the medium speed and high speed ones.
This is commonly caused by the force of gravity, such as blood falling from a finger or hand.
(2) Medium speed splash.
This type of blood pattern is usually caused by some kind of force or movement. This blood pattern is commonly seen in heartbeat type attacks. The blood is being moved or transported by something more than gravity and less than high velocity.
One key note to remember with this type of blood spatter is that during any type of blunt force trauma, the first blow or blow does not create any type of blood pattern. It is not until the actual trauma has begun to bleed from the wound that a second blow is delivered, causing the blood to forcibly disperse or flake off the weapon. A good rule of thumb is that the bigger or more blunt the weapon, the smaller the blood drops will be.
(3) High speed blood splash.
This type of pattern is produced by a tremendous external force. The easiest way to describe this type of pattern is often called a mist or spray. High speed patterns are commonly created by gunshots, explosives, and injuries from heavy machinery are often known to create a high speed pattern.
High velocity blood spatter droplets, due to their size, are often invisible to the naked eye. When investigating high velocity blood spatter, it is best to use a high intensity light and/or magnifying glass to locate and identify blood evidence due to the size of the blood droplets.
High velocity blood spatter can also be used to determine the distance of a subject involved in a firefight. When a bullet enters the body it causes an effect called “blow back”. This is blood blowing backwards in the direction the bullet came from. This fine mist will only travel a distance of two to three feet. You will often find small mist type droplets (high speed blood spatters) on the sleeve and sometimes on the chest of the subject firing the weapon.
This can be very important when trying to determine or dispute the distance between the shooter and the victim in cases where self-defense is claimed. In some cases to identify the shooter, since many times this blood evidence is very difficult to see and goes unnoticed. The suspect does not see blood on his clothing and does not clean it after being involved in the assault or homicide. Several reported suicide cases have been turned into homicide cases with this type of evidence after investigators found high-velocity blood spatter on the shirt sleeves of reporting parties.
Another type of blood evidence is a blood transfer. This is blood that has been carried from a source, such as hands, hair, and even clothing, and then transferred to another object.
When examining blood evidence, remember that blood will flow downward due to gravity and, being a fluid, it will take the path of least resistance. This will help you identify the position of your victim at the time of the injury and if the victim was moved in any way. Many times, the lack of evidence of blood or a “void” indicates that something has blocked the flow of blood or spatter. Again, this may indicate that the victim was moved or an item of evidence is missing from the scene.
An investigator using the blood evidence at the scene can also determine the angle of impact. Measuring the blood drops their width by their length (minus the tail) to determine the arcsine. This will determine the angle of impact. Once an investigator knows the angle of impact, this can help the investigator determine if the victim was standing, kneeling, or lying down at the time of the incident. Or even if the attack was moving.
This article is just the beginning and a very basic idea of using blood evidence in your investigations, however, as you can see, just the basics can help you with your case.