chapter 11 ppt - blair school...
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Forensic Science: Fundamentals & Investigations, Chapter 1 1
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Forensic Science: Fundamentals & Investigations, Chapter 11 2
Introduction to Death
l Death is a process, not an instant event l Medical examiners try to determine cause and
time using many factors. – Livor mortis – Rigor mortis – Algor mortis – Intestinal and stomach contents – Changes in the eye – Decomposition – Presence and life stage of insects
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Chapter 11 Death: Manner, Mechanism, Cause, and Time By the end of this chapter you will be able to:
l explain the development of livor, rigor, and algor mortis following death
l use evidence of these to estimate time of death l use evidence on stomach contents to estimate
time of death l use insect evidence to estimate time of death l explain how environmental factors can affect the
estimated time of death
Forensic Science: Fundamentals & Investigations, Chapter 11 4
Vocabulary
l Algor Mortis: the cooling of the body after death l Autolysis: the spontaneous breakdown of cells
as they self-digest l Cause of Death: the immediate reason for a
person’s death (e.g. heart attack, kidney failure) l Death: the cessation, or end, of life
Forensic Science: Fundamentals & Investigations, Chapter 11 5
Vocabulary
l Decomposition: the process of rotting and breaking down
l Instar: one of the three larval stages of insect development
l Larva (plural is larvae): immature form of an animal that undergoes metamorposis (e.g., maggots)
Forensic Science: Fundamentals & Investigations, Chapter 11 6
Vocabulary, cont.
l Livor mortis: the pooling of the blood in tissues after death resulting in a reddish color to the skin
l Manner of death: one of four means by which someone dies (e.g., natural, accidental, suicidal or homicidal)
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Forensic Science: Fundamentals & Investigations, Chapter 11 7
Vocabulary, cont.
l Mechanism of death: the specific body failure that leads to death
l Pupa (plural is pupae): the stage in an insect’s life cycle when the larva forms a capsule around itself and changes into its adult form
l Rigor mortis: the stiffening of the skeletal muscles after death
Mysterious Death at the Fair
How would you define: Manner of Death (see vocab) – Cause of Death (reason someone dies) – Mechanism of Death (what occurred in the body to cause death) –
Forensic Science: Fundamentals & Investigations, Chapter 2 8
Mysterious Death at the Fair
Manner of Death – Accidental Cause of Death – Food Poisoning/Water Contamination Mechanism of Death – Kidney Failure
Forensic Science: Fundamentals & Investigations, Chapter 2 9 Forensic Science: Fundamentals & Investigations, Chapter 11 10
Introduction
l Death – Heart Stops? – Brain Function stops? – Scientists/Doctors cannot come up with one
definition
– Death is a controversial topic l Cases
Forensic Science: Fundamentals & Investigations, Chapter 11 11
Introduction
l Death Process – Cells die due to lack of oxygen – Cells break down (autolysis)
l Enzymes & other cell contents spill out and digest surrounding tissues
Forensic Science: Fundamentals & Investigations, Chapter 11 12
The Manner of Death
l 4(5) Manners of Death 1. Natural
l Interruption and failure of body functions resulting from age or disease
2. Accidental l Unplanned events
3. Suicidal l Person purposefully kills oneself
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Forensic Science: Fundamentals & Investigations, Chapter 11 13
Manner of Death
l 4(5) Manners of Death, cont. 4. Homicidal
l Death of one person caused by another
5. Undetermined
Forensic Science: Fundamentals & Investigations, Chapter 11 14
It can be difficult to determine
l A man with a heart condition is attacked and dies from a heart attack. – Is the manner of death accident or homicide?
l An elderly woman dies after being kept from receiving proper health care by her son. – Is the manner of death natural or homicide? – Was it suicide or accidental?
l In the case of an overdose – Did the person overdose on accident or on purpose?
Forensic Science: Fundamentals & Investigations, Chapter 11 15
Manner of Death
l The most common manner of death is natural
Forensic Science: Fundamentals & Investigations, Chapter 11 16
Death
Cause and Mechanism of Death l The reason for the death is the cause of
the death.
Forensic Science: Fundamentals & Investigations, Chapter 11 17
Causes of Death
l Disease l Physical injury l Stroke l Heart attack
Forensic Science: Fundamentals & Investigations, Chapter 11 18
Causes of Homicide
l Bludgeoning l Shooting l Burning l Drowning l Strangulation l Hanging l Suffocation
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Forensic Science: Fundamentals & Investigations, Chapter 11 19
Mechanism of Death
l The specific change in the body that brought about the cessation of life is the mechanism of death.
l Example – Cause – Shooting – Mechanism - Loss of Blood (exsanguination),
Cessation of Brain Function l Example
– Cause - Heart Attack – Mechanism - Heart Stopping to Beat, Pulmonary
Arrest Forensic Science: Fundamentals & Investigations, Chapter 11 20
Time of Death
l Determining time of death is important. l If time of death is established, suspects…
– Can be proven innocent if they were known to be somewhere else
– Can remain suspects if they were in the vicinity
Forensic Science: Fundamentals & Investigations, Chapter 11 21
Time of Death
l Determined by: – Livor Mortis (death color) – Rigor Mortis (death stiffness) – Algor Mortis (death heat) – Stomach and Intestinal Contents – Changes of the Eye after Death – Stages of Decomposition – Insects
Forensic Science: Fundamentals & Investigations, Chapter 11 22
Time of Death—Livor Mortis
l Roughly - the color of death l Blood seeps down through tissues and
settles into lowest part of body – Settling is called lividity – Begins TWO hours after death
l Red blood cells break down, turn bluish-purple because of hemoglobin – Hemoglobin carries oxygen and gives blood red
color
Forensic Science: Fundamentals & Investigations, Chapter 11 23
Time of Death—Livor Mortis
l The discoloration that accompanies this becomes permanent after 8 hours – Will disappear between 2-8 hours
l Warmth accelerates the process l What a person is wearing can also effect
– Wristwatches and belts will impede blood flow l Lividity can determine if body was moved in
the first 8 hours - dual lividity
Forensic Science: Fundamentals & Investigations, Chapter 11 24
Time of Death—Rigor Mortis
l Roughly - death stiffness l At death, skeletal muscles cannot relax l Without oxygen, calcium accumulates in these
muscles l The muscles become stiff l Starts 2 hours after death l This starts in the head and works its way down to the
legs l At 12 hours after death, the body is at its most rigid
state.
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Forensic Science: Fundamentals & Investigations, Chapter 11 25
Time of Death—Rigor Mortis
l After about 15 hours, the muscle fibers begin to dissolve, and softening begins.
l This stiffness will have disappeared for the most part after 36 hours.
l If a body has no visible signs of rigor, it probably has been dead less than 2 hours or more than 48.
l If the body exhibits rigor only in the head and neck, the time of death is just over 2 hours.
Forensic Science: Fundamentals & Investigations, Chapter 11 26
Time of Death—Rigor Mortis
Many factors affect when rigor mortis sets in and how long it lasts:
– Ambient temperature l Cooler the body slower the onset of rigor l Warmer the body onset of rigor is faster because reactions
happen faster at high temperatures – The weight of the body
l Body fat stores oxygen will slow down rigor – The body’s clothing or lack of it
l Clothes hold in heat so a clothes body will go into rigor faster
Forensic Science: Fundamentals & Investigations, Chapter 11 27
– Any illness the person had at the time of death l Dead person dies with fever - rigor happens faster l Dead person has hypothermia - rigor happens slower
– The level of physical activity at the time of death l Person was exercising or struggling rigor will happen faster
– Exercise increases body temp – Exercise decreases oxygen availability
– Sun exposure l Body exposed to direct sunlight will be warmer
Forensic Science: Fundamentals & Investigations, Chapter 11 28
Time of Death—Algor Mortis
l Roughly - Death heat l In death a body no longer generates warmth and
begins to cool down. l To find the standard temperature of a corpse, a
thermometer is inserted into the liver. l Body heat is lost at about 1 to 1.5 (F) degrees an
hour. – After the first hour to 12 hours after death the loss of
heat is 0.78ºC (1.4ºF) – After the first 12 hours 0.39ºC (0.7ºF)
Forensic Science: Fundamentals & Investigations, Chapter 11 29
l Time of death determined by temperatures calculations is expressed as a range of time.
l Outside environment determines how fast the body loses heat
Forensic Science: Fundamentals & Investigations, Chapter 11 30
Time of Death - Stomach and Intestinal Contents
l In general, 4-6 hours for the stomach to empty contents into small intestine
l Another 12 to leave small intestine l 24 hours after meal was eaten to leave large
intestine
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Forensic Science: Fundamentals & Investigations, Chapter 11 31
Time of Death—Stomach and Intestinal Contents
Based on these specifics, give an estimate for each of these on how much time has passed since the meal was eaten: 1. Food is still present in the stomach. (0-2 hours
after last meal) 2. The stomach is empty but food is found in the
small intestine. (4-6 hours after meal) 3. The small intestine is empty but waste is present in
the large intestine. (12 or more hours after meal)
Forensic Science: Fundamentals & Investigations, Chapter 11 32
Time of Death—Stages of Decomposition
l Within 2 days after death – Cell autolysis begins – Green and purplish staining occurs from blood
decomposition – Skin marbled appearance – Face discolored
Forensic Science: Fundamentals & Investigations, Chapter 11 33
Time of Death—Stages of Decomposition
l After 4 days – Skin blisters – Abdomen swells with carbon dioxide
Forensic Science: Fundamentals & Investigations, Chapter 11 34
Time of Death—Stages of Decomposition
l Within 6-20 days – Corpse bloats because bacteria feeding on
tissues – Chest and abdominal cavities burst and collapse – Fluids leak from body openings – Eyeball and tissues liquefy – Skin sloughs off
Forensic Science: Fundamentals & Investigations, Chapter 11 35
Time of Death—Stages of Decomposition
l Speed of decomposition depends on age, size of body, nature of death – Sick people decompose faster – Overweight people decompose faster – Naked bodies decompose faster – Perfect temperature - 21-37ºC (70-99ºF)
l Higher temperatures dry out body to preserve l Lower temperatures prevent bacterial growth
Forensic Science: Fundamentals & Investigations, Chapter 11 36
l Moist environment rich in oxygen speed up decomposition
l Decompose quickly in air, slower in water or buried
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Forensic Science: Fundamentals & Investigations, Chapter 11 37
Time of Death—Insects
l Besides recording data about the environment at a crime scene, a forensic entomologist collects insect evidence.
l Within minutes of a death, certain insects arrive to lay their eggs on the warm body. Blowflies are a common example.
l As a corpse progresses through the stages of decomposition, other kinds of insects arrive.
Forensic Science: Fundamentals & Investigations, Chapter 11 38
Time of Death—Insects
l Blowfly eggs can be found in the moist, warm areas of a corpse within 8 hours after death.
l They will have progressed to the 1st of their 3 larva stages (illustration of one shown above) within 20 hours.
l By the 4th or 5th day they will have progressed to the 3rd of their 3 larva stages.
Forensic Science: Fundamentals & Investigations, Chapter 11 39
Time of Death—Insects
4. By the 8th or 12th day the larvae will migrate away from the corpse to a dry place.
5. Becoming pupa and immobile within 18-24 days, they will change from white to dark brown.
6. By the 21st-24th day the pupa cases will split open and adult blowflies (illustration of one shown above) will emerge.
Forensic Science: Fundamentals & Investigations, Chapter 11 40
Time of Death—Insects
l Because scientists know how long it takes for the various stages of development at given temperatures, forensics entomologists can determine when the insects arrived.
l Because life cycles are affected by fluctuations in the daily environmental conditions, insect evidence cannot provide an exact time of death.
l Insect evidence, nonetheless, can yield a close estimate.