7 Things You Didn’t Know About Blood Spatter Analysis
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Whether you’re an up and coming forensic analyst or just someone who can’t get enough of CSI, chances are you have heard a thing or two about blood spatter analysis. This field involves using the physics of fluids to help to determine the events of a (usually) violent crime by analyzing the placement of the blood droplets at the crime scene.
But even if you have seen countless television detectives rely on blood sprayed on the ceiling of a gory crime scene, there are probably a few things you do not know about the history and process of blood spatter analysis. Keep reading to learn more.
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The first modern study of blood stains occurred in 1895.
Blood spatter analysis, more professionally termed bloodstain pattern analysis (BPA), is not a new technique in the investigation of brutal crimes. In fact, it is thought to have been studied to some degree for centuries. However, the first surviving modern study of BPA occurred in 1895 when Eduard Piotrowski from the University of Krakow published a paper entitled “On the formation, form, direction and spreading of blood stains resulting from blunt trauma at the head”. The rather gruesome study that Piotrowski undertook involved covering one corner of room with white sheets and studying the blood patterns that appeared as he beat rabbits to death.
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2. The Sam Sheppard case, which is thought to have been the inspiration for the television series and subsequent film The Fugitive, was instrumental in expanding the use of blood spatter analysis techniques in the U.S.
On July 4th, 1954, Marilyn Sheppard, wife of prominent neurosurgeon Dr. Samuel Sheppard, was found bludgeoned to death in the Bay Village, Ohio home that the couple shared. Although Dr. Sheppard claimed to be asleep downstairs when he awoke to his wife’s cries and tried to stop the intruder from killing her, he was convicted of second-degree murder. His conviction was overturned by the U.S. Supreme Court in 1966 and he was granted a new trial, during which he was found not guilty. Testimony from the University of California at Berkeley biochemistry professor and forensic science pioneer Dr. Paul Kirk was thought to be integral to the new verdict. The crime scene was extremely bloody and the only blood found on Dr. Sheppard the morning the body was found was on one knee of his pants, which was not at all consistent with the idea that he was the perpetrator. Since that trial, blood spatter analysis has become much more widespread in the criminal court system.
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3. There is a difference between blood spatter patterns, blood drip stains, and blood transfer patterns.
Although they are each a part of the forensic branch of blood spatter pattern analysis, there are distinct differences between blood spatter patterns, blood drip stains, and blood transfer patterns. Blood spatter patterns are what most people generally think of when it comes to blood spatter. These droplets of blood have been acted on by forces other than gravity, either being cast off of a weapon, or spraying from a victim onto a surface. The shape and size of these droplets can help to determine the positioning of a victim, the type of weapon used, and the force used in the crime. On the other hand, blood drip stains appear when only gravity works on the blood. It may fall from an open wound on a victim or perpetrator, or may drip off of a piece of clothing or a weapon. These types of patterns can help determine in which direction and at what speed the person or object was moving at the time of the blood drip. Finally, blood transfer patterns occur when blood moves between objects by way of a conveyance like a hand, shoe, or piece of fabric. These could be the result of a struggle, or an attempt of a perpetrator to clean up or escape quickly.
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4. The surface where the blood lands can have a tremendous impact on the interpretation of the blood spatter.
Just as the motion of an object or person can determine what a blood spatter pattern looks like, so can the surface onto which the blood spatters. For instance, the same blood spattered on bedsheets, which would absorb blood and therefore distort the patterns, will look much different than the pattern that would exist on a pane of glass, which would cause no distortion, or even a concrete floor, which could lead to ‘satellite’ blood droplets. Blood spatter analysts must take into account the surface as well as the trajectory of the blood in order to determine the facts of the crime scene.
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5. BPA is perhaps most often used to confirm or refute the statements of witnesses or suspects present at the commission of a crime.
While blood spatter analysis can be extremely effective in determining the placement of perpetrators, victims, and weapons during the course of a violent crime, rarely are blood spatter analysts called on to make these assertions on their own. Rather, blood spatter is most often used as a tool to support or refute eyewitness testimony. For instance, a suspect may argue that they acted in self-defense during the commission of a crime, but a prosecutor may be able to call a blood spatter analyst that can offer their expert opinion that the victim was sitting or laying down – hardly on the attack – when the crime was committed, thereby refuting the suspect’s account.
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6. A human must lose approximately 40% of his or her total blood volume before they are at risk for death from blood loss.
A typical male has between 5 and 6 liters of blood while a typical female has between 4 and 5 liters. This amount of blood accounts for approximately 8% of a person’s total body weight. When a person loses more than 1 liter of blood, they are likely to become unconscious. But more than 1.5 liters and death quickly becomes a risk.
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7. Blood spatter analysis can be essential in determining the type of weapon used during a crime.
There are many reasons an investigator may not know what type of weapon was used during a violent crime. Perhaps a murder was committed by the weapon was hidden or destroyed along with the body. Or perhaps a body is so badly injured that it is impossible to tell how exactly the murder occurred. The different shapes and sizes of blood spatter on the surrounding area can determine the force, weight, and shape of the weapon. For instance, medium-velocity stains are generally caused by a blunt object, a fist, or even a violent spray from a severed artery while high-velocity spatter that creates tiny droplets is more likely to be from a gunshot wound.
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