POST-MORTEM INTERVAL

April 21, 2015

How do investigators determine time of death?

Watch a case study …

POSTMORTEM INTERVAL (PMI)The postmortem interval is the time since death.

In the video we just watched, what was the PMI?

About 12 hours.

How did the investigator determine it?Through rigor mortis and the ‘back story’ (e.g. when the wife left, the presence of

tea).

POSTMORTEM INTERVAL (PMI)

The postmortem interval is the time since death.Investigators can estimate this time using the following factors:

Body temperature Environmental conditions (temperature,

humidity, etc.) Body condition (blood pooling, stiffness,

decomposition) Presence of scavenger / decomposer

insectsOther environmental clues (e.g. a stopped watch), witnesses, and patterns of behavior are

also used!

BODY COOLINGAlgor mortis is the cooling of the body after death.

The most accurate way to determine the temperature of a body is to use a rectal thermometer or to put a thermometer in the liver of the body.

Typically, the rate of body cooling follows this formula:

Time (hrs) = Problem 1: Police discover a body alongside a road on a cool fall morning. They use a rectal thermometer to determine that the internal temperature of the body is 75.2 oF.

Approximately what is the PMI? 15 hours

BODY COOLINGAlgor mortis is the cooling of the body after death.

The most accurate way to determine the temperature of a body is to use a rectal thermometer or to put a thermometer in the liver of the body.

Typically, the rate of body cooling follows this formula:

Time (hrs) = Problem 2: A body is found in a parking garage. During autopsy, the medical examiner sticks a thermometer into the liver of the victim to determine that the internal temperature of the body is 87.6 degrees F.

Approximately what is the PMI? 7.2 hours

BODY COOLINGAlgor mortis is the cooling of the body after death.

The most accurate way to determine the temperature of a body is to use a rectal thermometer or to put a thermometer in the liver of the body.

Typically, the rate of body cooling follows this formula:

Time (hrs) = Problem 3: What should be the internal temperature of a body that died 9 hours ago?

84.9 oF

BODY COOLINGAlgor mortis is the cooling of the body after death.

The most accurate way to determine the temperature of a body is to use a rectal thermometer or to put a thermometer in the liver of the body.

Typically, the rate of body cooling follows this formula:

Time (hrs) =

This formula is most useful within the first 12 hours, but can sometimes be used within the first 36 hours. What determines the limit of its use?

Ambient temperature

Problem 4: If the outside temperature is 95, what temperature will a body be after 6 hours?95 – the body

won’t cool below ambient temperature!

BODY COOLINGWhat factors might change the rate of heat loss of a body?

Ambient temperature

Clothing

Whether the body is wet

Wind

Surface area to volume ratio

(colder = faster loss)

(more = slower loss)

(wet = faster loss)

(windy = faster loss)

(children = faster loss)

LIVIDITYLividity, or livor mortis, is purple or red discoloration caused by the pooling of blood after death. Indicates position of the body (and whether it was

moved): Blood pools lower in the body due to gravity, -but- does not pool anywhere that touches the ground or

is otherwise compressed In what position did this person die?

How do you know?

On her back. Lividity seen on back, except on areas (middle of back and buttocks) that touched the ground

LIVIDITYLividity, or livor mortis, is purple or red discoloration caused by the pooling of blood after death. Indicates position of the body (and whether it was

moved): Blood pools lower in the body due to gravity, -but- does not pool anywhere that touches the ground or

is otherwise compressed

Lividity begins at about 2 hrs

Becomes ‘fixed’ at 12 hrs

(marks will remain, even if

body is moved)

RIGOR MORTISRigidity, or rigor mortis, is the stiffness of muscles after death.

Muscles contract – and stay in contracted position for hours – due to chemical changes in muscle tissue

Begins approximately 2 hours after death, starting with small facial muscles and spreading to larger muscles

o Fades after 20-30 hours due to muscle decomposition, disappearing first from small muscles and then from larger muscles

Rule of thumb: 12 in, 12 out

ESTIMATING PMI1. A body was found outside in a ditch. The

internal body temperature matched that of the ambient temperature – 85 degrees. The body showed signs of lividity and had rigor mortis in all muscles.

What is the PMI? Explain your reasoning.Approximately 12 hours.

• Rigor mortis is at its peak (still in all muscles), which takes about 12 hours.

• Body temp indicates that it has been more than 9 hours

• Lividity indicates that it is more than 2 hours PMI. If the marks remain unchanged after moving the body, then it will indicate that more than 12 hours have passed.

ESTIMATING PMI2. A body was found outside in a ditch. The internal body temperature matched that of the ambient temperature – 85 degrees. The body had purple marks and white splotches due to blood pooling; these marks remained in place even hours after the body was moved. The arms and legs were somewhat stiff, but the smaller facial muscles were flexible.

What is the PMI? Explain your reasoning.Approximately 20-30 hours.

• Rigor mortis waning – only present in large muscles. Rigor mortis fades in 20-30 hours.

• Body temp indicates that it has been more than 9 hours

• Lividity is fixed, which indicates that it is more than 12 hours PMI

CLOSURE1. What were our objectives today, and

what did you learn?

2. What was our learner profile trait, and how did we demonstrate it?

3. How does this relate to our unit question?

EXIT TICKET1. A woman returned home from an

overnight trip to find her husband dead. The temperature of the body was 92.6 OF. There were few signs of lividity, but the facial muscles had signs of rigor mortis.

What is the PMI? Explain how each piece of evidence contributes to your answer.