Forensic Science
Name: TEACHER KEY
A. Death
a. Death is the cessation or end of life.
b. It is characterized by irreversible stopping of blood circulation and brain activity.
c. When the heart stops beating, oxygen is deprived from body cells and they begin to die, a process
known as autolysis.
i. Once enough cells die and begin to break down, life cannot be restarted.
d. In cases of suspicious or unnatural death, a pathologist conducts post-mortem examination, called an
autopsy.
i. Autopsies are conducted to determine the:
1. Manner of death- means by which they died
2. Cause of death- the reason they died
3. Mechanism of death- specific body failure
4. Time of death- when they died
B. Manner of Death
a. Five categories of manner of death can appear on death certificates:
i. Natural
1. Failure of body functions due to old age or disease.
2. Most common manner of death on death certificates.
ii. Accidental
1. Result of unplanned event, such as car accident or fall.
iii. Suicidal
1. Intentional killing of oneself.
iv. Homicidal
1. Death caused by another individual; murder.
v. Undetermined
1. Manner of death cannot be determined.
C. Cause and Mechanism of Death
a. Cause of death (COD) is the reason a person died.
i. Natural causes include disease, cancer, physical injury, stroke, heart attack etc.
ii. Homicidal and suicidal causes include shooting, burning, poisoning, hanging, drowning,
suffocation, etc.
b. 'Proximate cause of death' refers to an underlying cause of death, as opposed to the final cause.
i. For example, if someone is exposed to large amount of radiation then develops cancer, the
proximate cause of death is exposure to radiation.
c. Mechanism of death describes the specific change in the body that brought about the cessation of life.
Examples:
i. If someone has been shot, they may die from loss of blood, called
exsanguination (bleeding to death).
ii. If someone has a heart attack, they may die from pulmonary arrest (heart
stopping).
iii. If someone is strangled, they may die from asphyxiation (lack of oxygen).
d. Cause and mechanism of death are often stated together.
i. For example, a death certificate of someone in a car accident might read “massive trauma to the
body lead to pulmonary arrest”.
D. Time of Death
a. During an autopsy, the forensic examiner wants to determine when the person died.
i. A time of death helps forensic detectives include or exclude suspects based on their alibis or
location at that time.
b. In order to approximate the time of death, pathologists look at many factors:
i. Livor Mortis
1. Livor mortis refers to “death color”.
2. As body decomposition begins, blood settles in the lower parts of the victim’s body. Red
blood cells break and release hemoglobin, which turn purple as they spill out of cells.
Wherever these pools of blood settle, the skin takes on the purple coloring.
a. The pooling of blood is known as lividity.
i. Begin 2 hours after death.
ii. Between 2-8 hours after death, the color will disappear when the skin is
pressed on.
iii. After 8 hours, the discoloration becomes permanent.
iv. Temperature also affects livor mortis. Hot temperatures speed up the
process; cool temperatures slow it down.
1. As a result, when forensic detectives analyze a crime scene,
they should record the temperature.
3. Livor mortis not only helps approximate time of death, but also indicates the positioning
of the body during the first 8 hours of death.
a. For example, if all discoloration is on the front of the body, it indicated the
person was lying face down.
b. Discoloration on many parts of the body can show that a body was moved from
one location/position to another.
ii. Rigor Mortis
1. Rigor mortis refers to “death stiffness”.
2. It is caused by lack of oxygen to cells and calcium buildup in the muscles, causing stiff
muscles and joints.
3. Rigor mortis begins in the head about 2 hours after death, and slowly works down the
body and legs.
a. Stiffness peaks at about 12 hours.
b. As the cells dissolve during autolysis, the stiffness will slowly disappear.
c. Stiffness completely disappears around 36 hours.
4. A dead body that is not stiff has probably been dead less than 2 hours or more than 48
hours.
5. However, forensic experts must keep in mind that other factors can affect this timeline:
a. Cooler temperatures slow the onset of rigor mortis; warm temperatures speed
it up.
i. Clothing on a victim can affect this; a naked victim cools faster, which
slows rigor mortis.
ii. Illness can also affect this. Victims with a fever prior to death will
experience faster rigor mortis. And hypothermia slows the process.
iii. Sun-exposure may also provide warmth and increase rigor.
1. Also, if a victim struggled or exercised prior to death, they will
likely have less oxygen and also be warmer, again accelerating
rigor. Oppositely, a sleeping victim will have slowed rigor.
iv. Overweight individuals usually have more fat, which stores more
oxygen, causing slower rigor mortis rates.
iii. Algor Mortis
1. Algor mortis refers to “death heat” and describes a body’s temperature loss after death.
2. When a person is alive, the body maintains homeostasis and regulates a constant
temperature.
3. After death, the body no longer can maintain its heat and it begins to cool down.
4. To record the temperature of a corpse, forensic investigators insert a thermometer into
the liver.
5. A body cools at a rate of about 1.4 degrees per hour immediately after death, then
slows to 0.7 degrees per hour after about 12 hours, until it reaches the same
temperature as the environment.
6. As with other factors, outside temperature, clothing, and body fat can also affect algor
mortis.
iv. Stomach and Intestinal Contents
1. Time of death can also be estimated by
looking at the digestive tract and its contents.
2. It takes about:
a. 4–6 hours for the stomach to empty
its contents into the small intestine
b. 12 hours for the food to leave the
small intestine.
c. 24 hours from the time a meal is
eaten until all undigested food is
released from the large intestines
3. The location of food in the digestive tract
helps scientists estimate how long after a
person ate, that they died.
v. Changes in the Eye
1. Following death, the surface of the eyes dry out.
2. If the eyes were open at death, a thin film will appear on the eyes in 2-3 hours. If the
eyes are closed, it takes about 24 hours for this film to appear.
E. Insects
a. Insects are so useful in crime investigation there is a whole branch devoted to it
called forensic entomology.
b. Duties of a forensic entomologist are to:
i. Record detailed crime scene conditions (temperature, moisture, wind)
ii. Collect insect evidence on, above, below, and surrounding the corpse
iii. Determining an estimate for the postmortem interval or PMI (the time between death and the
discovery of the body)
1. If insects from another region are found on a corpse, it suggests that the corpse may
have been moved and provide important evidence to determine a primary crime scene.
iv. Testify in court to explain insect-related evidence found at the crime scene
c. The first stages of decomposition give off an odor which attracts insects to lay their eggs on the body
within minutes of death.
i. Ex. Blowflies are one of the first insects to arrive at a body. Their four stages
of development (egg  larva/instar  pupa  adult) are very useful in
determining time of death.
d. As a corpse progresses through stages of development, other insects will arrive.
i. Wasps, flies, beetles, moths, ants, bees, and mites
e. Scientists have collected information on stages of development at given
temperatures for all types of insects known to feed on corpses. This allows forensic
entomologists to estimate time of death based on insect evidence gathered at a
crime scene.
i. The University of Tennessee Anthropological Research Facility,
nicknamed the “Body Farm”, investigates human decomposition.
Bodies are placed in different settings throughout the facility and left
to decompose. The bodies are exposed in a number of ways in order
to provide insights into decomposition under varying conditions.
F. Stages of Decomposition
a. Bodies begin to decompose shortly after death and do so in five predictable stages:
i. Fresh
1. Begins almost instantly after death.
2. Livor, rigor, and algor mortis occur.
3. Autolysis, or self-digestion, begins as lysosomes break down and release their digestive
enzymes into the cell.
4. Visible changes caused by decomposition are limited during the fresh stage, although
autolysis may cause blisters to appear at the surface of the skin.
ii. Bloat or Putrefaction
1. This stage of death is mostly due to the activities of microorganisms; first intestinal
flora, then saprophytic bacteria and fungi.
2. Characterized by the production of gases which gives rise to the bloated appearance of
the decomposing body and strong odor.
3. Skin turns a greenish color as blood decomposes.
4. Skin may break apart and fluids can flow out from the openings.
iii. Active Decay or Black Putrefaction
1. This stage is recognizable by a great loss in mass, due largely to feedings by maggots
and other insects. Parts of flesh may be black and corpse gives off an even stronger
odor.
2. As gases escape and the body leaks decomposition fluids, the body may collapse.
3. The end of this stage is marked by the dispersal of the maggots from the body.
iv. Advanced Decay
1. The body begins to dry and preserve itself; most of the flesh is gone.
2. Odor and insect activity decrease.
3. Body may form a wax layer known as the adipocere.
v. Dry Remains or Skeletonization
1. Final stage. Recognizable by a loss of everything on the body but dried up bone.
b. Speed of Decomposition depends on many factors:
i. Age
1. Young decompose faster than elderly.
ii. Size of body
1. Overweight people decompose faster than average.
iii. Clothing
1. Naked decompose faster than clothed.
iv. Health
1. Sick decompose faster than healthy.
v. Environmental Conditions
1. Bodies decompose fastest in 70-99 oF
2. Higher temperatures dry out corpses and preserve them; lower temperatures prevent
bacterial growth and slow decomposition.
3. Bodies decompose faster in air, and slower in water or soil.