Editor’s Note: This article is part of an ongoing series about how different aspects of forensic science can help during death investigations. Read about livor mortis and entomology (the science of analyzing insect evidence).
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Rigor mortis, which refers to the stiffening of a body after death, can assist investigators in determining the estimated time at which someone died. Also, as with livor mortis, rigor mortis may help indicate whether a body has been moved after death.
Rigor mortis is the result of the death of cells in the muscle fibers of the human body, which leads to chemical changes in those fibers that cause shortening, or stiffening, of the muscles. A living human produces Adenosine Triphosphate (ATP) which allows muscles to relax. When a person dies, the body no longer makes ATP due to lack of circulating oxygen and, thus, the muscles enter a state of constant contraction.
In locations where temperatures and environments are moderate, rigor mortis begins to set in one to two hours after death. The stiffening affects the small, involuntary (i.e., autonomic) muscles of the body first, including those in the eyelids, around the internal organs, and heart. Next, rigor mortis is evidenced in small voluntary muscles, such as the jaw and neck. It eventually spreads throughout the entire body, from the neck down. It usually reaches its peak at approximately 12 hours after death. A body generally remains in full rigor for 12 or so more hours before the stiffening subsides and completely dissipates by the 36-hour mark.
How Temperature Affects Rigor Mortis
There are several factors that can accelerate or decelerate the typical process of rigor mortis. Very warm climates will speed up the stiffening process and cold environments will retard its progression. For example, the effects of a chilly environment would be evidenced in the body of someone who drowned in very cold water. In a case like this, the body may not even begin the rigor mortis process until it is removed from the water.
Not only does the surrounding ambient temperature affect the onset of rigor mortis, but the internal temperature of the body at death does as well. Having a high fever at the time of death will accelerate the progression of rigor mortis. Additionally, exercising vigorously, or experiencing a rush of adrenaline, at the time of death will speed up the process as there is significant depletion of ATP in the muscles during these circumstances. The use of stimulants, such as cocaine or amphetamines, prior to death renders the same result.
Real Life Examples of Rigor Mortis
This is a helpful example of how rigid muscles become when succumbed to rigor mortis. The photo shows the decedent on the floor with both arms facing upwards, defying gravity. Based on the angle of the arms, the body is in full rigor mortis. However, it’s clear he did not die in this position. If he had, gravity would have resulted in his arms resting on the ground. Likely, the responding medical examiner/coroner in this case turned this man’s body to illustrate the effects of full rigor mortis.
One case in which the intensity of rigor mortis helped determine time of death is that of 22-month-old Cooper Harris. Harris was left strapped in his car seat by his father on a blistering day in June 2014. His father maintains the incident was a tragic accident and the result of him forgetting to drop his son off at daycare. When Harris’ body was discovered and removed from the vehicle, it was in full rigor mortis. First responders removed the boy’s body and placed it on the ground in hopes of achieving resuscitation. However, it was too late to save the toddler.
Images from a news article shows the lower portion of the boy’s body as it lay on the ground, legs bent as if he was still sitting in the car seat. The stage of rigor mortis combined with the over 80F-degree temperature (which caused the interior of the car to be over 100F) were consistent with the father’s account that the boy had remained in the car for approximately seven hours. Normally, it would take roughly 12 hours for rigor to reach its full state, however the increased temperature sped up the process.
When I interned with the Office of the Chief Medical Examiner in New York City, I distinctly remember a death scene I attended where the decedent had passed away while sitting on the toilet. When I arrived, his body was on the floor, but his hips and legs were bent at a 90-degree angle, clearly in full rigor. The angle of his lower extremities made it obvious that he’d been positioned on the toilet at the time of death, which had occurred approximately 12 hours before. At some point after death, gravity took its toll causing the body to fall to the floor.
The phases of rigor mortis can be extremely helpful in piecing together the circumstances and timing of a death. Rigor is one of the many potential clues examined by crime scene technicians, forensic pathologists, and detectives during an investigation to determine the proper manner of death (i.e., homicide, suicide, accident, or natural causes). It may also verify or refute a witness or suspect statement and can sometimes indicate whether a body has been moved after death. It is a valuable indicator that cannot be overlooked.
About the Author: Jennifer Bucholtz is a former U.S. Army Counterintelligence Agent and a decorated veteran of the Iraq and Afghanistan wars. She holds a Bachelor of Science in criminal justice, Master of Arts in criminal justice and Master of Science in forensic sciences. Bucholtz has an extensive background in U.S. military and Department of Defense counterintelligence operations. While on active duty, she served as the Special Agent in Charge for her unit in South Korea and Assistant Special Agent in Charge at stateside duty stations. Bucholtz has also worked for the Arizona Department of Corrections and Office of the Chief Medical Examiner in New York City. She is currently an adjunct faculty member at American Military University and teaches courses in criminal justice and forensic sciences. Additionally, she is a licensed private investigator in Colorado. You can contact her at IPSauthor@apus.edu. For more articles featuring insight from industry experts, subscribe to In Public Safety’s bi-monthly newsletter.