Understanding Blood Spatter as Evidence
If you turn your television on in the evening it is very likely you will find a television show where investigators are using some type of forensic or scientific method to collect or identify evidence. If you’re not into the crime television shows you can turn to the real television shows where they analyze a crime scene that has already been solved and the suspect is convicted using forensic evidence collected at the scene.
Having over thirty years of a law enforcement investigative background and working 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 type of forensic or scientific evidence if you want a conviction.
In this article I will explain some of the very basics of blood evidence and how to interpret the clues the blood evidence leaves.
Blood pattern’s and the interpretation of bloodstain patterns are very convincing evidence when used by an investigator that understands and can identify and explain them.
Blood evidence is most commonly used by a law enforcement investigators in criminal cases having experience and training in blood spatter. However, if a private investigator is assisting in a defense case with an attorney or working with a family in a wrongful death case and he/she has an understanding and knowledge of blood patterns, it can just as useful.
Some of the items blood evidence can show is movement and momentum during an attack, the type of weapon, and if 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) Low velocity spatter.
This occurs with a minimal amount or no force. The blood pattern is much larger than those of medium velocity and high velocity.
This is commonly caused by the force of gravity, such as blood dropping off a finger or hand.
(2) Medium velocity spatter.
This type of blood pattern is usually caused by some form of force or movement. This blood pattern is commonly seen in beating type attacks. The blood is being moved or carried by something more than just gravity and less than high velocity.
A keynote to remember with this type of blood spatter is that during any type of blunt force trauma the first strike or blow does not create any type of blood pattern. It is not until the actual trauma has started to bleed from the wound and a second blow is struck, causing the blood to disperse out from the force or is cast off the weapon. A good rule of thumb is the larger or blunter the weapon the smaller the blood droplets.
(3) High velocity blood spatter.
This type of pattern is produced by an external tremendous force. The easiest way to describe this type of pattern is often referred to as a mist or spray. High velocity patterns are commonly created by gunshots, explosives, and injuries from heavy machinery have often been known to create a high velocity pattern.
High velocity blood spatter droplets, due to their size, are often times invisible to the naked eye. When investigating high velocity blood spatter it is best to use a high intensity light and/ or a magnifying glass to locate and identify the 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 shooting. When a bullet enters the body it causes an effect called “blow back”. This is blood blowing back in the direction the bullet came from. This fine mist will only travel a distance of two to three feet. You will often find tiny mist type droplets (high velocity blood spatter) on the sleeve and sometime chest of the subject firing the weapon.
This can be very important when attempting 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, as often times this blood evidence is very difficult to see and goes unnoticed. The suspect does not see any blood on his clothing and fails to clean it after being involved in the assault or homicide. Several reported suicide cases have turned into homicide cases with this type of evidence after investigators found high velocity blood spatter on the reporting parties shirt sleeves.
Another type of blood evidence is blood transfer. This is blood that has been carried from one source such as hands, hair and even clothing then transferred to another object.
When examining blood evidence, remember that blood will flow down due to gravity, and being a fluid, it will take the path of least resistance. This will assist you in identifying the position your victim at the time of the injury, and if the victim was moved in any manner. Often times the lack of blood evidence or a” void” indicates that something has blocked the blood flow or spatter. Again this can indicate 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. By measuring the blood droplets 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 to determine if the victim was standing, kneeling, or laying down at the time of the incident. Or even if the attack was moving around.
This article is only the beginning and a very basic idea of using blood evidence in your investigations, however, as you can see, just the basic can assist you with your case.
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Stuart M Robinson