Under the Microscope
Welcome to “Under the Microscope,” Killer Nashville’s very own exclusive Forensics Corner. We will unearth, demystify, and bring you interesting, factual information about the world of forensics from experts in various fields. From dead bodies, to suspicious substances, to computers with a mind of their own, this column will explore the macabre, gory, and unexplainable with the truth in scientific terms for writer’s to use at their will.
This is the second installment in a three-part series by physician, author, former Killer Nashville Guest of Honor Dr. D.P. Lyle. Through the imagined lens of a coroner, he shares critical information about the business of death and the elements of a great investigation.
The Coroner’s Most Important Determinations: Part 2
By D.P. Lyle
In the first part of this series I discussed the critical determination of the Cause and Manner of Death, and what gets the authorities’ attention. Now let’s take a look into the all-important Time of Death.
Time of Death: Part 1
One of the most important determinations made by the Medical Examiner (ME) is the time of death. This alone can exonerate or focus suspicion on a suspect. It can substantiate or refute witness and suspect statements. It can literally make or break the case.
The timing of death is both an art and a science and requires that the ME use several techniques and observations to make his estimate. The sooner after death the body is examined, the more accurate this estimate will be. The changes that a body undergoes after death occur in widely variable ways and with unpredictable timeframes. There is no single factor that will accurately indicate the time of death. It is always a best guess.
To help with his estimation, the ME employs various observations and tests. These include:
- Body Temperature
- Rigor Mortis
- Livor Mortis (Lividity)
- Degree of Putrefaction
- Stomach Contents
- Corneal Cloudiness
- Vitreous Potassium Level
- Insect Activity
- Scene Markers
Let’s look at each of the techniques.
Body Temperature: Normal body temperature is 98.6 degrees Fahrenheit. After death, the body loses or gains heat progressively until it equilibrates with that of the surrounding medium. Under normal circumstances a corpse will lose body heat at a rate of approximately 1.5 degree/hour. This means that a corpse with a core temperature of 92 degrees has been dead about 4 or 5 hours. Sounds simple enough. Unfortunately, it’s not quite that straightforward. The 1.5-degree-per-hour factor varies, depending upon the environment surrounding the body, the size of the corpse, clothing, and other factors. For example, a body in a temperate room will lose heat much more slowly than will one in an icy, flowing stream. A body in a hot environment such as an enclosed garage in Phoenix in August where the ambient temperature could be 125 degrees or more will actually gain heat. The key is that the corpse will lose or gain heat until it reaches equilibrium with its environment. Once the body reaches ambient temperature, this factor is no longer useful.
Rigor Mortis: Rigor mortis is the stiffening of a corpse after death and is due to chemical reactions that take place within the muscle cells after death. This chemical reaction is the loss of adenosine triphosphate (ATP) from the muscles. ATP serves as energy for muscular activity and without it our muscles could not contract. The presence and stability of ATP depends upon a steady supply of oxygen and nutrients, which are lost with the cessation of cardiac activity that occurs at death. When the ATP levels fall, the muscles contract and stiffen, producing the rigidity of rigor.
This rigidity is first detectable in the small muscles of the face, neck, and hands and then progresses to the larger muscles. The rigor begins in about 2 hours and the entire process takes about 12 hours at which time the body is completely stiff. This is called the rigid stage and tends to remain so for another 12 hours. The process then reverses itself with rigidity being lost in the same fashion, beginning with the small muscles and progressing to the larger ones. This process requires another 12 or so hours. The muscles are now flaccid (relaxed) and this is termed the flaccid stage of rigor mortis.
A good general rule is 12-12-12. Under normal conditions, rigor begins in about 2 hours, maximizes at about 12 hours, remains unchanged for 12 hours (rigor stage), and resolves over the next 12 hours (flaccid stage). So, rigor is only useful in the first 36 hours or so after death.
This rule assumes “normal” circumstances. If the death was associated with violent activity such as drowning of the victim fighting or running for his life, then the ATP can be consumed during these activities and rigor can appear much more quickly, even sometimes almost instantly at death—a condition often termed cadaveric spasm. In a drowning, the rigor might be universal while in the fleeing victim it might be confined to the legs, the body part doing the work and depleting its ATP supply prior to death.
Also, cold conditions might delay rigor while warmer ones can hasten it. See? It’s not that simple.
Livor Mortis: Lividity is a purplish hue of the tissues and is caused by the stagnation of blood in the vessels that occurs after the heart stops beating. Gravity then causes the stagnant blood to settle into the dependent (lower) areas of the body. This means that a supine corpse will develop lividity along the back and buttocks. It typically appears between 30 minutes and 2 hours after death and reaches its maximum by 8 to 12 hours. Initially, rolling the body to a different position can shift this discoloration, but by 6 to 8 hours, it becomes fixed. This means that rolling the body to another position will not result in a shifting of the discoloration. The reason is that after about 6 to 8 hours the blood vessels in the area begin to breakdown and the blood seeps from the vessels and stains the surrounding tissues. As opposed to the blood that remains within the vascular system, this blood in the tissue is fixed in position. The ME can use shifting and fixed lividity to estimate time of death and to determine if the body has been moved or repositioned, something the dead do not do without assistance.
As with rigor, the onset and the fixing of lividity is often slowed in a cold environment and quickened in a warmer one.
Next time, we will look at the other factors listed above that the ME uses to estimate the time of death.
D. P. Lyle is the Macavity and Benjamin Franklin Silver Award winning and Edgar, Agatha, Anthony, Scribe, and USA Best Book Award nominated author of many non-fiction books (Murder & Mayhem; Forensics For Dummies; Forensics & Fiction; More Forensics & Fiction; Howdunnit: Forensics; and ABA Fundamentals: Understanding Forensic Science) as well as numerous works of fiction, including the Samantha Cody thriller series (Devil’s Playground, Double Blind, and Original Sin); the Dub Walker Thriller series (Stress Fracture; Hot Lights, Cold Steel, and Run To Ground); and the Royal Pains media tie-in novels (Royal Pains: First, Do No Harm and Royal Pains: Sick Rich). His essay on Jules Verne’s The Mysterious Island appears in Thrillers: 100 Must Reads and his short story “Even Steven” in ITW’s anthology Thriller 3: Love Is Murder.
Along with Jan Burke, he is the co-host of Crime and Science Radio. He has worked with many novelists and with the writers of popular television shows such as Law & Order, CSI: Miami, Diagnosis Murder, Monk, Judging Amy, Peacemakers, Cold Case, House, Medium, Women’s Murder Club, 1-800-Missing, The Glades, and Pretty Little Liars.
D.P. Lyle has become a regular feature at Killer Nashville. Join us and learn more.