Discussions about forensic science and medicine

Monday, June 19, 2006

When did the murder take place

Many a time I have been called by the police to places where dead bodies are lying and I am asked to tell them when a particular person was done to death. This is a very important question for the police to know. Imagine a person found dead in a hotel room at 10.00 pm by a waiter. Visitors' register and statements of various hotel employees reveal that four people met that man on that day at 10 am, 1 pm, 3 pm, and 7 pm respectively. Obviously, the murder was committed by one of them. Many might imagine the last visitor to be the murderer, because, had an earlier visitor murdered the man, the next visitor would have informed the police. But this is not necessarily so. A man might knock at the door, get no answer and return. Also, a visitor with a criminal record may have been too afraid to inform about the murder, even if he had discovered the dead body. Thus, it becomes very important to tell exactly when the person died.

We use a very ingenious technique to do that. A law of physics says that a hot body always comes back to the temperature of its surroundings. Thus if you keep a glass of hot milk on the table, after sometime, the milk cools down. Our bodies also work similarly. While living, however, the various life processes keep the human body warm and do not let the body cool. At the time of death, all life processes stop and the body starts cooling down. All human beings have a temperature of 98.40 Fahrenheit. The surrounding temperature in shade varies from 600 to 800 Fahrenheit depending upon the weather. SO, after death, the body tends to cool down and come to the temperature of the environment.

We do not take the temperature of the dead body by keeping the thermometer in the mouth, as is done in living beings. This is due to various reasons. For one thing, we are interested in taking the core temperature of the dead body and not the surface temperature. Core temperature is the temperature of the internal organs of the body, while surface temperature is the temperature of the skin. Surface temperature is generally lower than the core temperature. Thermometer in the mouth or axilla gives the surface temperature, which is not of much interest to us. Another reason why we do not take the mouth temperature is that the jaws become stiff after death. So, it becomes very difficult to open the mouth of a dead person and if someone forcibly inserted the thermometer in the mouth, there is every likelihood of the thermometer getting cracked.

After death, the body starts cooling in a well defined way. In summers, a dead body cools by about 0.750 Fahrenheit ever hour and in winters, it cools faster- by about 1.50 Fahrenheit every hour. The first thing that we do after arriving at the scene of crime is to insert a thermometer deed in the rectum of the dead body (see figure 1). We insert it almost 4-5 inches deep. This gives us the core temperature of the body, in which we are interested. In fact, there are several ways to take the core temperature of the body, but this is the simplest. Many doctors prefer to make a small incision (about 0.5 cm), just below the rib margin on the right side of the body and insert the thermometer deep in this nick (see figure 2). Since the liver lies just below this nick, the thermometer gets inserted in the liver. This procedure also reveals the core temperature but many doctor do not prefer this method, because it injures the liver. Later, when the body is opened for post mortem, some difficulties may be encountered in assessing the injuries to the liver, if there are any. This is because the insertion of the thermometer may have interfered with the injuries already present in the liver.

Some other doctors prefer to take the brain temperature. For this, they drill a hole in the skull and then insert the thermometer deep inside the brain. In the case of females, some doctors prefer to insert the thermometer in the vagina and take the vaginal temperature. However the most common site remains the rectum, as shown in the figure.

We already know the rate of cooling of the body after death. Suppose I am called by the police at 10.00 pm to a hotel room, where a dead body is lying. I will first of all take the rectal temperature. Suppose the temperature is found to be 870 Fahrenheit. It is the month of February and I know that dead body cools at the rate of 1.50 Fahrenheit every hour in winter months. The loss in temperature is (97.4-87)0 or about 10.40 Fahrenheit. Dividing it by 1.5, I get the number of hours the person has been dead to be seven. I deduct 7 hours from 10 pm (the time when I am making the examination) and arrive at the correct time of murder- 3 pm. The police summons the visitor who called the murdered man at 3 pm, and detailed questioning begins.

Simple, isn't it? But as Sherlock Holmes used to say, all deductions seem simple when they are explained. They are difficult only till they remain unexplained.

Anil Aggrawal
Professor Forensic Medicine
Maulana Azad Medical College
New Delhi

3 Comments:

Blogger Dr Gaurav said...

Dear Sir,
I have a couple of comments to make regarding this murder mystery.
Firstly, is it a reliable formula to calculate time since death? What is the accuracy of this formula?
Secondly, Reddy’s textbook (I’m not though fully confident of quoting it!) gives a formula as- Time Since death = Normal body temp. – Rectal temp. (degree Centigrade) ÷ Rate of fall of temp. per hour, where the rate of fall is 1.5 0C/hr for the first 6 hrs and roughly 1 0C/hr for the next 6 hours. Of course, it does not take the environmental temp. into consideration! Although your formula also does the same kind of calculation, but it takes environmental temp. into consideration as the rate of fall of temp. is different for summer and winter. Why are the two formulae similar but based on different logic?
Your comments, please.
Regards,
Dr Gaurav Aggarwal

9:34 PM

 
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2:23 PM

 
Blogger Ruby Purl said...

If someone was found dead in their home and their liver temp was 83 degrees Fahrenheit and the room was 83 degrees Fahrenheit, and an extreme degree of rigor mortis was evident in all parts of the body, with post mortem lividity on the right side which was consistent with the position that the body was found; can you estimate the time of death? Liver temp was taken at 2:10p.m. Location was Los Angeles, CA and the month was August. Weather was warm. Cause of death was multiple stab wounds.

1:02 AM

 

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