Imagine that you're watching your favorite crime drama show. A murder has taken place. The police and forensic experts are looking for clues to catch the killer. One of the most important clues to solving the crime is determining when the victim died. The expert looks at the body, checks the body temperature, and examines the body's position.
After a thorough examination, the expert then states the approximate time of death. The question is, how does a forensic expert calculate the time of death? The time of death is not the exact time that a person died.
It is instead a time frame in which the person could have died, based on the evidence presented. Forensic scientists calculate the time of death using many techniques. Their first go-to method is to study the physical changes that happen in the body after death.
So what are these signs? There are four post-mortem signs that tell a great deal about time of death. These are physical observable changes that occur in the body in the first 24 to 48 hours after the heart stops beating. and the nervous system shuts down. The first sign, palormortis.
As this heart stops beating, the circulation of blood throughout the body decreases. The organs farther away from the heart, like the skin, stop receiving blood. This gives a corpse the pale, lifeless appearance that we associate with death. This paleness, which appears 15 to 30 minutes after death, is called palormortis.
It is one of the first identifiable signs of death. The second sign, algormortis. Humans are homeothermic, which means we maintain a constant internal body temperature. This constant average temperature is maintained by balancing the heat produced in the body with the heat lost. The circulatory system is an important mechanism by which humans maintain an average internal temperature of 37 degrees Celsius.
Heat is produced primarily through the various metabolic reactions happening in our body. This produced heat is dissipated from deeper organs, such as the liver and brain, to the outer parts, such as the skin, through the movement of blood. Under the first layer of skin, the epidermis supplies a network of capillaries.
These capillaries allow heat produced by the body to be released into the air. Without the heart beating, blood cannot distribute heat and regulate body temperature. This leads to the body temperature reaching equilibrium with the external temperature. If the temperature is less than 37 degrees Celsius outside in the first hour after death, then the temperature of the body will decrease by 2 degrees and then continue to decrease by one degree every hour.
Algormortis is not an accurate way to back calculate the time of death however, as it varies based on external conditions, such as weather, and is affected by whether the corpse was wearing clothes or not. The third sign, rigor mortis. This sign is one of the most important signs when it comes to determining the time of death.
Rigor mortis, which literally means stiff death, is the contraction of the muscles in the body after death. Before rigor mortis, all the muscles relax in a step called primary flaccidity. This happens because, after death, brain activity decreases until it completely stops.
Without the brain giving muscles a signal to contract, the muscles remain in a relaxed state. Primary flaccidity lasts for 1-2 hours after death. The first muscles to relax are those in the eyelids, fingers, and toes. In this stage, the corpse usually releases urine and gas. as muscles controlling urination and passing gas are relaxed.
Primary flaccidity is followed by rigor mortis. Muscles stiffen up in rigor mortis because of cells being broken down by digestive enzymes. This cellular breakdown is a normal part of body decomposition and is called autolysis.
The breakdown of cells makes holes in the boundary of the cell and its compartments. This releases calcium ions from the separate compartment within the cell where they are stored. This calcium is crucial for initiating contraction.
During normal living conditions, a signal from the nervous system triggers the calcium to release from its compartment. Another factor causing rigor mortis is the lack of ATP, the energy-giving molecule in the muscle cells. Once calcium initiates muscle contraction, myosin, a protein molecule that moves things around in the cell, binds to actin, a long chain of proteins that form the skeleton of a cell.
Once the myosin binds to actin, it uses the energy from ATP to pull the actin. making the muscle fiber shorter and shorter with each pull. Immediately after death, muscles can still produce ATP. Muscles have reserves of glucose in the form of the polysaccharide glycogen, which it breaks down, in the absence of oxygen, to provide ATP. This ATP is used up in muscle contraction, but the muscles also need ATP to relax.
This means that the actin and myosin will remain contracted until the muscle is completely decomposed. Rigor mortis starts in the same order that primary flaccidity does. with the eyes and fingers, and slowly progresses to the rest of the body. Rigor mortis reaches its peak 12 hours post-mortem.
After that, the muscles begin to relax in the same order that they began contraction. After rigor mortis comes a second cycle of relaxation called secondary flaccidity, which is due to muscle degeneration. Digestive enzymes break down the proteins in the muscles, including the muscle contracting machinery. Forensic experts use this progression of muscle relaxation and stiffening to estimate the time of death. They will check to see which parts of the body have stiffened and make an estimate based on what they find.
It is more reliable than algor mortis as it isn't as affected by external conditions. The fourth sign, liver mortis. After death, blood is subject to the forces of gravity, now that the heart isn't moving it around any longer. It pools wherever the forces of gravity is strongest.
This starts about 15 to 30 minutes after death and starts to become visible two hours after death. Lividity, as it is called, starts to become fixed after six hours, as the blood vessels begin to break down. After 8 to 12 hours, a purple coloration develops.
This purple color develops because the deoxygenation of hemoglobin forms deoxyhemoglobin, which has a purple-blue color. Liver mortis can be very useful for determining time of death. Once lividity is fixed, it doesn't fade, even when the body is moved. If a part of the body came in contact with a firm surface that obstructs the blood flow, an impression of it will show on the skin that is surrounded by pooled blood. The color or pattern of lividity can allow forensic scientists to guess not only what the time of death could be, but also the cause of death.
Lividity in the extremities, such as the fingers, would suggest that the body was upright, as opposed to lividity developed on the back, which would suggest a horizontal position. These four signs are commonly used together in order to estimate the time of death. The time of death is not 100% accurate, however, because of so many other factors, such as the environment, weather, clothes, or whether the victim was moved. Forensic experts will most likely give a time frame rather than an exact time. So, the next time you're watching a crime drama, don't forget to be that guy and point out all the loopholes you see.