READ: Death Investigation

Post Mortem Interval

Mortality

Mortality refers to death, or the fact that people are subject to death. One of the grimmer aspects of crime scene investigation is dealing with a scene where a victim has died. If a body is found the main question that investigators will want answered, is when the person died. Depending on the state of the body, this can range anywhere from minutes to years. There are many different specialists that may become involved depending on the state of the body. These specialists are trained in how to determine the time of death based on different information they can find from the body.

We will be learning more about each of these specialties this unit, but the main ones are forensic pathology, anthropology, and entomology. If the body has not decomposed to the point that it is mostly a skeleton, a forensic pathologist, or a medical examiner will perform an autopsy to determine how and when they died. If the body is skeletalized and anthropologist can use information from the bones to determine when, and possibly how a person died. Entomologists are people who study insects, they can be involved if there are insects present on a body.

Post Mortem Interval

After a person has died it is the goal of many people to determine the post mortem interval. The post mortem interval is the time that has passed since a person died. There are many different changes that take place after a person dies. Some of the more immediate ones may be noticed at the crime scene, and will later be noted by the medical examiner.

Estimating the PMI

Rigor Mortis

Rigor mortis is a condition that develops soon after a person dies. The muscles in the body become rigid and the body becomes stiff. This condition develops within the first 24 hours and typically subsides after 36 hours. This time frame can help give a rough estimate of the time of death. For example, if a body is found to have rigor mortis, you can usually assume that the person died 24-36 hours ago. It is important to understand that this condition can develop more rapidly if temperatures are hot.

Algor Mortis

Algor mortis happens when the body begins to lose heat. After the person has died, the body temperature decreases until it reaches room temperature, or the temperature where the body is lying outside. Bodies will typically lose 1-1.5 degrees fahrenheit per hour. By taking the temperature of the body, this can give a rough estimate of the post mortem interval. For example, normal body temperature is 98.6 degrees fahrenheit, so if a body is found to be 80 degrees you can estimate that the person has been dead around 12 - 18 hours.

Algor mortis can also be affected by other factors that you need to take into consideration. The clothes the body is wearing can hold in more heat depending on the type of clothes. The temperature where the body is can also make the process faster or slower. If the body is larger it can release heat more slowly. All of these factors must be considered when estimating the time of death based on algor mortis.

Livor Mortis

Livor mortis begins right after a person dies and continues for about 12 hours. Livor mortis happens when the blood in the body pools in the areas closest to the ground. This starts to happen as soon as the heart stops pumping after death. When the blood pools it creates a darker purple or red splotches on the skin. If the body was restricted by clothing or something under the body, blood will not pool in that area. After about 12-16 hours the coloring is fixed and would no longer change if the body was moved.

Livor mortis is especially useful because it can help investigators determine if a body was moved after death. If the patterns don’t match up to where the body was found, it is possible that the body was somewhere else when death occurred. It is also possible to make an estimation about the post mortem interval from livor mortis based on whether or not the pattern is fixed. Sometimes investigators will push on the skin to see if the coloring will go away. If it does, the body has been there less than 12 hours. Livor mortis can also be affected by temperature, so it is important to keep this in mind when estimating the time of death.

Vitreous Humor

The vitreous humor is the fluid in the eyeball. After a person dies the levels of potassium in the vitreous humor increases. Investigators at the scene can draw fluid from the eye and test the amount of potassium present. This can help them determine the time since death, but it is also impacted by temperature.

Stomach Contents

The contents of the stomach can also provide clues about the time of death, and sometimes even the cause of death. The contents of the stomach can be examined as part of an autopsy. If food is found in the stomach that usually means the person died just a few hours after they last ate. If the stomach is completely empty that usually means the person died at least 6 hours after they last ate. The medical examiner can also look at the small intestine. If no food is present in the small intestine it has typically been at least 12 hours since the person ate.

Sometimes the stomach contents can also contain clues about how a person died. They might contain partially digested pills indicating that the death was a poisoning or overdose. The stomach contents could also be tested for suspected drugs or other toxins that might be involved in the death.

Decomposition

Decomposition

After a few days real decomposition starts to set in. After decomposition begins algor, livor, and rigor mortis are generally no longer helpful. Several different processes start to take place as the body’s own enzymes start to break down and as bacteria and insects start to decompose the body.

Putrefaction

Putrefaction is the process in which the tissues and organs of the body are broken down by bacteria and fungi. The bacteria or fungi will actually consume the proteins and tissues of the body resulting in liquefaction of the organs. This process typically releases gasses and can cause the body to bloat. It also caused odors. After about 2-3 days the body will start to discolor and turn a greenish color beginning with the abdomen and eventually going out towards the limbs. After about 2 weeks the body will be very bloated with the gasses made from the bacteria and after about 4 weeks the body will be severely decomposed and unrecognizable.

The putrefaction process is obviously dependent on the temperature where the body is. In hotter temperatures the process will proceed more quickly. This is why morgues and funeral homes store bodies at lower temperatures. Lower temperatures can greatly slow or even stop the decomposition process from occurring.

Skeletonization

After the bodies tissues have all decomposed the skeleton is visible. The process of skeletonization can take anywhere from about a month to a few years depending on the climate and conditions the body is in. The temperature, presence of water, air, or chemicals can all influence how long the process takes.

Sometimes bodies can decompose in different ways in certain conditions. In order for decomposition to take place bacteria and fungi need to be able to survive. Most bacteria and fungi require oxygen to live. So if a body is exposed to conditions where oxygen is absent, decomposition may not take place in the typical way. Mummification and adipocere are both examples of how this can happen.

Mummification

A body can become mummified if the conditions are right. In order for mummification to occur the body must usually be in dry conditions. Mummification can also occur if the body is in extremely cold conditions or conditions in with there is no oxygen. A body can also be mummified if it is exposed to certain chemicals. Basically a mummified body is dried out.

Adipocere

Adipocere is a waxy substance that is formed from body fat. Sometimes the fat in a body will become hard and waxy. It is usually a gray or white color. This typically takes a few months to form, but once it has formed, it can last for years. The face, the abdomen, and fatty areas are the mostly likely to form adipocere. Women, infants, and obese people are more likely to form adipocere because they have a higher concentration of body fat. In order for adipocere to form, the conditions must be right. It usually forms when the body is exposed to high levels of moisture and low oxygen, such as in muddy or wet ground.

Cause and Manner of Death

Cause and Manner of Death

The cause of death and the manner of death are two different things. The cause of death is the physical condition that actually led to death. Physical conditions are usually diseases or injuries. Examples of causes of death would be things such as heart attack, gunshot wound, influenza, stroke, etc. The manner of death is determined by the medical examiner. There are five different possible manners of death:

• Natural

• Accidental

• Homicide

• Suicide

• Undetermined

Body Farms

Body Farms

Body farms are research facilities where anthropologists study what happens as humans decompose under different conditions. There are several body farms in the United States. The first body farm was started by Dr. William Bass at the University of Tennessee. There is still a body farm run by the university today. The body farm will place bodies in different situations and record what happens as they decompose. This is very helpful to law enforcement agencies during an investigation. They study what happens to bodies under a variety of circumstances such as when a body is wrapped in bags, or when it is in the sun versus the shade, or if it is buried in a shallow grave, etc.

This research provides investigators with a time frame of how decomposition would proceed based on the conditions the body is in. The body farm uses human bodies that people decide to donate to the farm for research. They also sometimes use pig carcasses during the research as well. They study things such as, how insect life cycles proceed in a body, what insects are there, how long stages of decomposition take, and how bones become scattered after a period of time.