Introduction to Forensic Science

1
Introduction to Forensic Science

• Forensic Pathology

2
The autopsy provides forensic evidence.

• Forensic Pathology is the branch of medicine
  which analyses victims of crime scenes medically.
• They are the last physician for the deceased and
  their role is to discover and interpret the
  evidence left during the autopsy.

3
Forensic Pathology

• Pathology, the study of disease, is the broadest
  of the medical specialties.
• Pathologists dont treat patients nor do surgery
  themselves- they consult with primary care and
  specialist physicians.
• Forensic Pathologist is a medical doctor with
  10-15 post secondary training.

4
Anatomic Pathology

• Diagnosis of disease and injury by the gross and
  microscopic examination of tissue specimens
• Biopsies
• Organs
• pap smears
• bone marrow aspirates
• blood smears.
• The anatomic pathologist is also the one who
  performs autopsies.

5
Clinical Pathology

• Clinical pathology deals with the medical
  laboratory where the pathologist serves as
  medical director.
• The pathologist bears ultimate responsibility for
  medical laboratory test results.

6
Role of the Pathologist

• Determine type of wound
• Measure the dimensions (length, width, depth)
• Position relative to anatomical landmarks
• Determine initial location if wound involves
  cutting, slashing, etc.
• Determine height of victim, other contributing
  factors like heart problems.

7
Analysis of Wounds

• Not every crime victim is murdered.
• Pathologists can contribute to proof of the
  severity of a crime or that a crime actually
  occurred in some cases for a living victim.
• Some victims are too young to testify and some
  are too severely injured to remember the crime.
• Wounds provide evidence of the crime.

8
Wound Categories

• Bruises (or contusions)
• Abrasions (or grazes or scratches)
• Lacerations
• Incised wounds
• Puncture (or stab) wounds
• Gunshot wounds

9
Gunshot Wounds

• This will be discussed with ballistics talk

10
Bruises

• A bruise is "a hemorrhage into tissues produced
  by the escape of blood from blood vessels".
• Bruises may be found in the skin, muscles, and
  internal organs.

11
Bruises

• Bruises are typically produced by a blunt force
  impact, such as a blow or a fall.
• They may also be produced by squeezing or
  pinching, where the force is applied gradually
  and then maintained.
• Hickies or "love-bites" are superficial bruises.

12
Natural Bruises

• Bruises may occur in a variety of natural
  diseases in which there is an abnormality of the
  clotting mechanism of the blood, e.g. scurvy
  (vitamin C deficiency), leukemia, alcoholic liver
  disease.
• This bruising is "spontaneous" because the injury
  which produces it is so insignificant as to
  typically pass unnoticed.
• The presence of such natural disease will
  exaggerate the bruising effects of any trauma.

13
Problems with Skin Bruises

• Delayed appearance
• Ageing (relative)
• Site of Trauma
• Shape of object
• Degree of force
• Post-mortem bruises
• Post-mortem lividity

14
Classic Causes of Bruises

• Finger pad bruises battered babies, manual
  strangulation
• Different ages repeated assaults
• Shoulders and arms forceful restraint
• Wrists and ankles dragging
• Inner thighs forceful intercourse
• Chest resuscitation
• Bruising is uncommon in Suicides

15
Bruises

• The extent of bruising is inversely proportional
  to the sharpness of the impacting object.
• Bruises may be associated with other blunt force
  injuries such as abrasions and lacerations.
• As a general rule bruising is not associated with
  incised wounds or stab wounds where there is a
  free flow of blood from the cut blood vessels
  rather than leaking into the tissues.

16
Site of Trauma

• In contrast with abrasions, the location of a
  bruise does not necessarily reflect the precise
  point of injury.
• Leaking blood will follow the path of least
  resistance and gravity.

17
Delayed Appearance

• Deep bruises may have delayed appearance at the
  skin surface. Deep bruises may require as long as
  12 or 24 hours to become apparent, and some may
  never do so
• The more superficial the source of bleeding, the
  sooner the discoloration will be seen on the skin
  surface.
• In a living victim, a second examination in one
  or two days may show bruising.
• In the dead, a further examination one or two
  days after the original autopsy may show bruises
  which were not previously seen and reveal
  previously faint bruises.

18
Autopsy and Bruising

• Bruising in Deep Tissue
• 1. Possibly life-threatening
• 2. Sometimes no external injury
• 3. Revealed in autopsy
• Documenting Bruising
• 1. Photography
• 2. Notes

19
Degree of Force

• The size of a bruise is an unreliable indicator
  of the degree of force causing it.
• However, a heavy impact is likely to produce a
  large bruise and a light impact to produce a
  small bruise.
• If bruising is slight, it is reasonable to assume
  that the degree of violence was slight.

20
Determining Degree of Force in Bruise Patterns

• Location
• Some areas of the body bruise more easily than
  others. The face bruises more readily than the
  hands.
• Bruising occurs more readily in loose tissues and
  where there is a large amount of subcutaneous fat
• Bruising is less apparent where the skin is
  strongly supported by fibrous tissue or if the
  muscle tone is good.

21
Determining Degree of Force in Bruise Patterns

• Age
• Infants and the elderly tend to bruise more
  easily than young and middle aged adults.
• Infants have loose and delicate skin, and the
  abundant subcutaneous fat.
• Elderly have degenerative changes in the tissues
  which support the small blood vessels of the skin
  and subcutaneous tissues.
• Gender
• Women bruise more easily than men because they
  have more subcutaneous fat and this is
  particularly true of obese women.
• Natural Disease
• Skin color

22
Causitive Object

• The shape of the bruise is most likely to reflect
  the shape of the causative object when the object
  is small and hard and death occurs soon after
  injury

23
Causitive Object

• A doughnut bruise is produced by an object with a
  rounded contour (e.g. baseball).
• Two parallel linear bruises result from a blow
  with a rod or stick
• Bruises can follow rounded contours if they are
  caused by a flexible object like a lash

24
Causitive Object

• Bruises produced by fingerpads as a result of
  gripping are usually larger than the fingerpads
  themselves.
• The pattern and location suggests the mechanism
  of causation
• On the neck in throttling
• On the upper arms in restraint.
• Such bruises are referred to as patterned.

25
Aging of Bruises

• Color changes a bruise goes through can give a
  rough estimate of time of injury
• Colors result from breakdown of hemoglobin from
  tissues
• Dark blue/purple (1-18 hours)
• Blue/brown (1 to 2days)
• Green ( 2 to 3 days)
• Yellow (3 to 7 days)
• This rate assumes person is healthy, however.

26
Aging Bruises

• While accurate estimation of the age of a single
  bruise is not possible, a fresh bruise can be
  distinguished easily from one which is several
  days old.
• Establishing that bruises are of different ages
  may be of medical importance where there is an
  allegation of repeated assaults
• Child abuse
• Wife beating
• Where pre-existing injuries need to be
  distinguished from those produced by a recent
  assault like a chronic alcoholic who was
  assaulted.

27
Post Mortem Bruises

• Bruising is a phenomenon of living tissue- since
  it usually requires circulating blood to push the
  blood from the veins.
• It isnt possible to tell bruises that occurred
  causing death from those that occurred minutes
  earlier. You can only say they occurred at or
  about time of death.

28
Post Mortem Bruises

• It requires considerable violence to produce a
  bruise post mortem or after death.
• These bruises are smaller relative to the degree
  of force used.
• Post mortem bruises are most readily produced in
  areas of hypostasis (post mortem lividity, livor
  mortis) or where tissues can be forcibly
  compressed against bone.
• A bruise can develop on the head after the body
  is left lying on the back.

29
Post Mortem Lividity (hypostasis, livor mortis)

• The settling, after death, of blood within the
  blood vessels under the influence of gravity.
• This results in a purplish discoloration of
  parts of the body that are lower while sparing
  areas of pressure contact - contact pallor.
• The pattern and distribution of lividity
  distinguishes it from bruising.
• A body found on its back has livor mortis on the
  dorsal (back) side with pale areas where the bone
  contacted the floor.

30
Decomposition

• Post mortem decomposition with its initial green
  discoloration of the anterior abdominal wall is
  readily distinguished from bruising.
• Putrefactive lysis of blood cells within the
  vessels and decompositional breakdown of the
  vessel walls results in diffusion of lysed blood
  into the adjacent tissues.
• Existing bruises are enlarged by this process.
• Later, putrefactive hemolytic staining of tissue
  may mask ante mortem bruising (e.g. in the neck
  muscles in case of choking).

31
Patterns of Injury

• Bruises to the knuckles of the hands, together
  with bruises of the eyelids, bridge of the nose,
  cheeks and lips, suggest a fist fight.
• Bruising around the eyes (spectacle bruises) may
  be produced by direct blows, but also commonly
  result from a fracture of the base of the skull,
  e.g. in vehicle collisions or gunshot wounds to
  the head
• They may also follow blunt impact to the forehead
  producing jolting of the eyeballs in their
  sockets with tearing of small orbital blood
  vessels.

32
Patterns of Injury

• Bruising of the genitalia and around the anus
  suggests sexual assault.
• Severe bruising of the genitalia, with or without
  laceration, can be produced by kicks.
• Counter-pressure bruising, with or without
  abrasion, to the back, (shoulder blades, sacrum
  and pelvis) suggests pressure against a firm
  surface as in forceful restraint on the ground.
• Similar bruising may be seen on boney prominences
  of the front of the pelvis.

33
Patterns of Injury

• In kicking assaults with the shod foot, bruises
  are invariably associated with multiple abrasions
  and lacerations.
• Gangs, individuals without weapons
• The bruises and abrasions may be patterned by the
  boot.
• Bruising is typically extensive and targeted on
  the face, neck, ears, groin, and kidney area.
• Internal bruising is usually severe.

34
Patterns of Injury

• Bruises are painful and therefore not commonly
  self-inflicted extensive bruising creates a
  presumption of assault.
• Accidents generally are unforeseen and the
  injuries they produce tend not to follow a
  recognizable pattern.
• Some places bruise easily accidentally though
  shins and hips.

35
Patterns of Injury

• Injuries in motor vehicle collisions almost
  invariably include abrasions and lacerations as
  well as bruises.
• Patterns of injury may allow reconstruction of
  incidents involving pedestrians or allow
  distinction between driver and front seat
  passenger.

36
Participation Question

• Give me an example of forensic usefulness of
  analysis of bruises.

37

• Abrasions
• Friction injury removing skin or tissue

38
Abrasions

• Side impact produces a moving abrasion
• Indicates direction.
• Trace material (e.g. grit).
• Direct impact produces an imprint abrasion
• Pattern of causative object.
• All abrasions reflect site of impact (in contrast
  with bruises).
• Assessment of age of abrasions is difficult.
• Post-mortem abrasions - Brown, leathery

39
Incised Wounds (Cuts, Slashes, Stab)

• Stab wounds or puncture wounds are penetrating
  injuries whose depth within the body is much
  greater than the dimensions of the wound on the
  body surface.
• Breach of the full thickness of the skin due to
  contact with a sharp edge.

40
Stab Wounds

• Forensic Importance
• Reflects sharp edge, not weapon type
• No trace evidence
• Bleeds profusely
• Hemorrhage and air embolism
• They can be produced by any long thin object
  which impacts the body with sufficient force to
  penetrate.
• The typical instrument is a knife, but any sharp
  pointed, or keen-edged object will work.

41
Stab Wounds Should be Described at Autopsy

• Site relative to local anatomical landmarks as
  well as its distance from the midline and above
  the heel (or below the crown of the head).
• Shape and Size including the dimensions with the
  wound edges closed back.
• Direction (approximately) in three dimensions.
• Depth of the wound track at autopsy.
• Damage to tissues and organs along the wound
  track.
• Effects of damage described above.

42
Stab Wounds Shape of Weapon

• A knife blade with a double edge will normally
  produce a symmetrical elliptical wound with both
  ends pointed, clean cut edges and without any
  associated bruising or marginal abrasion.
• A knife with a single-edged blade may show
  relative blunting ("fish-tailing") of one end of
  the entry slit. A single edged blade can produce
  a wound with two pointed ends, mimicking an
  injury from a double edged blade.
• A bayonet, which has a ridge along the back of
  the blade with a groove along each side, may
  produce a slit like an elongated letter "T".

43
Stab Wounds Shape of Weapon

• Stab wounds produced with relatively blunt
  instruments such as pokers, closed scissors and
  files, tend to bruise and scrape the wound
  margin.
• These blunter instruments also tend to lacerate,
  as well as cleanly penetrate, the skin the
  blunter the point of the instrument and the
  thicker its shaft, the more likely is the entry
  hole to become a ragged, often cross shaped
  split.
• Forensic Pathologist sometimes practices wound
  type The Body Farm.

44
Stab Wounds Degree of Force

• The most reliable estimate of blade width is made
  from the deepest wound with the shortest skin
  surface length.
• It is easy to over-estimate the amount of force
  required to produce a stab wound.
• The depth of a wound is not generally an
  indication of the degree of force used.

45
Stab Wounds Degree of Force

• The most critical factor is the sharpness of the
  point of the instrument relatively little force
  is required to produce a stab wound provided a
  knife with a sharp point.
• After clothing, the skin offers the greatest
  resistance to penetration once this is overcome,
  then the blade easily cuts into deeper tissue.

46
Stab Wounds Degree of Force

• The penetration of bone does imply a significant
  degree of force.
• The tip of the blade may break off when driven
  into bone and should be recovered for matching
  with the weapon.
• In estimating the force exerted by an assailant,
  consideration should be given to the possibility
  of counter pressure by the victim, e.g. running
  or falling forwards.

47
Stab Wounds Length of Weapon

• The depth of the wound (the length of the wound
  track, provides some indication of the length of
  the stabbing instrument).
• The wound track length may be less than the
  length of the instrument if the weapon was not
  thrust into the body to its full length.
• The wound track can be longer than the knife if
  there is force compressing tissues.

48
Stab Wounds Clothing

• Cuts on the clothing should be noted and
  correlated with injuries to the body.
• More than one cut on the clothing may correspond
  with a single injury to the body as a result of
  folds in the clothing.
• Cuts to the clothing may not exactly overlie
  corresponding wounds to the body.
• There may be stab or slash marks on the clothing
  without corresponding injuries to the body, e.g.
  "defense"-type slashes to the arms.

49
Stab Wounds Clothing

• Blood flow patterns on the clothing may indicate
  the position of the victim at the time of the
  stabbing.
• Blood drops on the tops of the shoes from a stab
  to the chest in a victim standing upright.
• Blood flow direction can change with movements of
  the body.
• Wound track can be indicated by undercutting and
  beveling of the external wound.
• Extrapolation from the direction of wound tracks
  to an opinion on the relative positions of an
  assailant and victim should be, since two
  potentially moving objects are involved.

50
Stab Wounds Cause of Death

• Most deaths from stab wounds are homicides.
• Homicidal stab wounds are usually multiple, since
  most wounds leave the victim capable of some
  resistance for a measurable time during which the
  thrusts are repeated.
• Single homicidal stabbings are often associated
  with drugged, drunk, sleeping, or otherwise
  partially incapacitated victims and are almost
  always aimed at the heart.

51
Stab Wounds Cause of Death

• Homicidal stab wounds to the chest are all likely
  to be deep, penetrating the chest wall, and more
  than one may be lethal.
• Stabs in the back strongly suggest homicide.
• In cases of multiple scattered stabs, the larger
  the number the greater the certainty of murder.
• There is often a sexual motive to deaths with
  this type of "over-kill".

52
Defense Stab Wounds

• "Defense wounds" are the result of the immediate
  and instinctive reaction of a victim to ward off
  anticipated injuries and may be seen in both
  homicidal and accidental deaths.
• Defense wounds result from raising the arm to
  ward off the attack or attempts to grasp the
  weapon.
• The resulting injuries may be stabs or slashes or
  both.

53
Defense Stab Wounds

• Attempts to grab the knife results in deep cuts
  to the palm of the hand and the palm side of
  fingers.
• With the hand in a gripping position the palm
  skin is loose and folded so that resultant cuts
  appear irregular and ragged.
• They may be duplicated by the thrust and
  withdrawal of the weapon.
• Penetration of the hand or arm is also a defense
  wound.
• The absence of defense wounds does not exclude
  homicide since the victim may be incapable of
  effective defense.

54
Suicidal Stab Wounds

• Suicide by stabbing is distinctive. The wounds,
  if multiple, have a location and direction
  accessible to the victim and are typically
  grouped in the "pit" of the stomach.
• Use of one hand is indicated by a consistent
  direction of penetration.
• Multiple wound tracks extending from the same
  slit in the skin reflects partial withdrawal of
  the weapon and further thrusts (possibly trial
  feelers), and suggests possible suicide.

55
Suicidal Stab Wounds

• Typically a suicidal stabbing is to the bare skin
  and the clothing may be removed or pulled aside
  to effect this.
• Defense wounds do not occur in suicide, although
  the sharpness of a knife may be tested by running
  the blade across the tips of the fingers.
• Multiple scattered wounds weighs against suicide
  unless there was serious mental illness.

56
Suicidal Stab Wounds

• Fatalities from a single stab wound can be
  difficult and such a wound may be homicidal,
  suicidal, or accidental.
• Autopsy findings should always be interpreted in
  the light of information concerning the
  circumstances and scene of death.
• If the stab wound was inflicted during a fight
  then the usual defense is that it was accidental,
  the victim having ran or fallen on to the weapon.
• The position and direction of the wound may help
  resolve the issue.

57
Stab vs Slash

• Stab wounds are deep and not wide.
• Slash wounds are wide and not deep.

58
Penetrating Wounds (Punctures)

• Breach in full skin thickness and depth is
  greater than length
• Long, thin, sharp or blunt object.
• If sharp object then equals "stab wound".

59
Lacerations (Tears, Splits)

• Splitting of the skin by the direct crushing of
  blunt trauma.
• Typically over bone, e.g. scalp, eyebrow,
  cheekbone.

60
Lacerations

• Distinguished from incised wounds by
• Adjacent abrasion/bruise
• Ragged edge
• Tissue bridges in depth
• Forensic Importance
• Not related to object shape
• Trace evidence
• Relatively little blood loss (except scalp)
• Rarely suicidal

61
Lacerations

• Typical Examples
• Stellate pattern from poker end
• Circles/crescents from hammer
• Y-shaped from metal rod
• Inside lips from blow to mouth.
• Stretching lacerations in vehicular accidents.

62
Bite Marks

• Double crescent of abrasions and bruises
• Early Examination, loss of definition
• Swab for saliva, photograph
• Comparative value
• Child abuse, sexual assault.

63
Assault

• Any type of wound, combinations
• Scattered, multiple directions, uniform force
• Defense injuries
• Several potentially lethal
• Clothing
• Secondary injuries

64
Order of Infliction

• Tentative or scattered first
• Fatal and grouped last
• Distant shots before close shots.

65
Accidental

• Any area, single, clothing
• Defense injuries
• Secondary injuries
• Check history (suicide attempts, assaults)

66
Blood Spatter

• Bruises and abrasions, none
• Lacerations, not much
• Incised and stab wounds, often profuse.

67
Strangulation

• Strangulation implies pressure to the neck, and
  deaths due to strangulation are therefore of
  immense forensic importance.
• It can be defined as a circumferential squeezing
  of the neck that is independent of the
  gravitational weight or suspension of the head.
• Manual strangulation
• Ligature strangulation
• Choke holds

68
Signs of Strangulation

• Obstruction of jugular veins with impaired venous
  return to the heart, leading to cyanosis (blue
  color), congestion (tissue swelling), and
  petechiae.
• Obstruction of carotid arteries.
• Stimulation of baroreceptors in the carotid
  sinuses and carotid sheaths.
• Elevation of larynx and tongue, closing the
  oropharynx.

69
Petechia

• Very small hemorrhages (ranging in size from a
  pinpoint to a pinhead), which occur in tissues,
  may be described as petechia, or petechial
  hemorrhages (from the Italian petecchia, which
  has the Latinized plural petechiae).
• These hemorrhages may also be described as
  punctate (from the Latin punctum, a point).

70
(No Transcript)
71
Manual Strangulation

• Usually caused by men against women, and rarely
  against another man since a large disparity in
  physical strength between the assailant and
  victim is needed.

72
Signs of Manual Strangulation

• Disc-like finger-tip bruises
• Abrasions
• Linear finger-nail scratches (from victim or
  assailant)
• Often limited signs of suffocation as fingers are
  more likely to probe deeper neck structures and
  cause reflex cardiac arrest

73
Signs of Manual Strangulation

• Sustained pressure may cause congestion and
  blueness of the tongue, pharynx and larynx
• Hemorrhage under the skin of the neck and
  bruising of the strap muscles
• Damage to the larynx - particularly the superior
  horns of the thyroid cartilage, and the greater
  horns of the hyoid bone

74
Ligature Strangulation

• Where a constricting band is tightened around the
  neck, there is usually gross congestion, cyanosis
  and petechiae in the face if the pressure is
  maintained for more than about 20 seconds.
• The ligature mark is a vital part of the
  evidence, as it often reproduces the pattern and
  dimensions of the ligature itself.

75
Ligature Strangulation

• If the assailant has removed the ligature from
  the scene, and is subsequently arrested, possible
  ligatures found on the assailant or in his home
  can be compared with the mark on the victim's
  neck.
• Some modern techniques involving computer imaging
  are being developed to assist in this comparison
  process.
• A rising peak indicating a suspension point, is
  seen in cases of hanging or suspension.
• Victims may struggle less than manual
  strangulation.

76
Choke Holds

• These include the so-called 'carotid sleeper' and
  'bar arm' choke holds that are sometimes used in
  law-enforcement situations, although they are
  increasingly being outlawed in many
  jurisdictions.
• There is often little or no external neck injury
  visible, while hemorrhages in the strap muscles
  can be more extensive and broader in nature.
• If the bar arm hold has been of sufficient
  strength, the airway may have been obstructed,
  leading to 'air-hunger', and lead to violent
  struggling on the part of the restrained person.

77
Asphyxia

• Smothering - the covering of the mouth or nose
  (or external occlusion) e.g. by a plastic bag or
  in overlay deaths (may see abrasions etc in a
  homicidal smothering if the victim could put up a
  struggle)
• Gagging - the tongue is pushed backwards and
  upwards, and the gag becomes saturated with
  saliva and mucus causing further obstruction.
• Foreign body obstruction (those at risk being
  children/ infants, the intoxicated and those with
  neurological difficulties with swallowing etc)
• Swelling of the airway lining (anaphylactic
  hypersensitivity reactions, or thermal/ heat
  injury).

78
Carbon Monoxide

• Carbon monoxide poisoning is a form of asphyxia
  that results when CO is breathed.
• Poorly ventilated houses with faulty heaters,
  housefires, and motor vehicle exhaust are the
  most common sources.
• Even small atmospheric concentrations of CO are
  dangerous, because CO binds to hemoglobin 200
  times more avidly than oxygen.
• Drowsiness and headache occur at
  carboxyhemoglobin concentrations between 10 and
  20.
• Levels from 20 to 30 can be fatal to persons
  with pre-existing cardiac or respiratory disease.
  
• Levels above 30 to 40 can be fatal to anyone.

79
Note the bright "cherry red" or bright pink
lividity to the hand.
80
Drowning

• Drowning may not produce extensive findings.
• In 10 to 15 of cases, intense laryngospasm may
  even prevent water from entering the lungs.
• In some cases, some of the plant material in the
  water is aspirated into a bronchus, as seen
  through microscopic examination.
• A frothy fluid may exude from mouth and nose.
• Prolonged immersion may produce skin wrinkling
  and slippage.

81
Drowning

• Decomposition is some times held back by a
  phenomenon known as saponification the process
  where certain soft tissues are said to saponify
  or literally to make soap.
• The process of saponification begins after
  decomposition has loosened and even partially
  removed a layer of skin. The underlying fatty
  layer is then exposed. This fat, in a warm, moist
  environment, undergoes a process called
  hydrolysis.
• These fatty acid tails from the fat layer combine
  with calcium and ammonium to form insoluble
  soaps.

82
Drowning

• Adipocere is made from the adipose layer of fat
  lying just under the skin.
• Adipocere appears as a grey-white waxy substance
  and its formation of adipocere inhibits further
  decomposition.
• Dry environments and the presence of oxygen
  inhibit adipocere formation. Adipocere usually
  indicates a postmortem interval of a least
  several months duration.

83
Role of the Forensic Pathologist in an Autopsy

• Cause of Death
• medical diagnosis denoting disease or injury
• Proximate vs. immediate.
• Mechanism of Death
• altered physiology by which disease/injury
  produces death (arrhythmia, exsanguination, blood
  loss)
• Manner of Death
• Homicide
• Suicide Not always easy to determine
• Accidental may involve human negligence
• Natural Causes disease or old age

84
Participation Question

• What is rigor mortis?

85
Normal Postmortem Changes

• rigor mortis
• livor mortis
• desiccation
• putrefaction
• autolysis

86
Rigor Mortis

• Stiffening of muscles seconds or minutes after
  death
• Rigor mortis results when ATP concentrations
  fall
• ATP relaxed muscles
• No ATP contracted muscles
• Rigor mortis stops when muscles begin to
  decompose 36 hours after death
• Rigor mortis is used to estimate time of death
  (more discussion later)

87
Livor mortis

• Livor mortis purplish discoloration of the body
  and organ surfaces
• Becomes visible 30 minutes to 2 hours after death
• Results from breakdown of hemoglobin heme
  leaking into extravascular tissues
• Livor mortis is also used to estimate time of
  death.

88
Other Normal Postmortem Changes

• Desiccation mucous membranes (lips, eyes)
  shrivel and look darkly colored
• time depends on location of the body,
  environmental conditions
• Putrefaction
• Greenish discoloration of skin
• Growth of bacteria unchecked by immune system
  causes gas production which may swell, rupture
  organs or make soft tissue appear swollen
• time again depends on environment of body (few
  days to weeks if colder)

89
Normal Postmortem Changes

• Autolysis cells begin to break open and ooze
  contents
• Liquefaction of soft tissues
• Proteins break down into amino acids which are
  further degraded by bacteria into biogenic
  amines
• this is what smells (putrescine, cadaverine)