Friday, April 15, 2011

Determining Time of Death

We have the dead body, we set up the perfect murder, planted forensic evidence, and of course, we have our suspects (including "red herrings").  That’s all we need, right?  Well, it always helps to know when the victim died, and for our investigators this is imperative in pinning the murder on the guilty.  So, how do they go about figuring out time of death (TOD)?

There are quite a few physical elements a Medical Examiner, and forensic investigator have at their disposal for making an accurate estimate.  If they get it wrong, the killer can have an alibi in place that otherwise wouldn’t be.  

The 3 main ways of determining TOD are:
- Body Temperature
- Rigor Mortis
- Lividity

Let’s examine these areas in more detail.

Body Temperature
The general rule is the body cools on average 1°C per hour, from the starting temperature of 37°C.  The rate at which the body cools depends on a lot of factors such as environmental temperature, humidity, whether the vic was dressed or not, age of the victim, and weight.  For example, an adult cools slower than an infant, as an obese adult would cool slower than a fit adult.

Also, in order to determine the rating of cooling more accurately, the temperature of the corpse may be taken at several different intervals.

Where is the temperature taken?
This isn’t for the squirmish (of course would you be reading this post if you were?), but one way the temperature is taken, is rectally.  Yes, you read that right.  In fact, I verified this fact from a few different sources.  Another way, which is one you may be more familiar with, is liver temperature.

Rigor Mortis
After death, all muscles relax, and then stiffen.

Good rule to remember with this one is 12-12-12.  Let me explain.  It takes 12 hours for the rigor to set in, 12 hours the body will be in full rigor, and 12 to come out.  It starts in the smaller muscles such as the eyelids, and face before spreading to the larger muscles.  There are factors that can affect the “formula” though, such as climate, illness, age, and weight.

Also known as “liver mortis”, and hypostasis, this is the process where gravity makes the blood settle.  This turns areas of the skin a dark blue, or purple. 

After @ 2hrs – the skin is bluish and blotchy
After 5-6 hrs - the blotches have joined up but the skin still goes white when pressed
After 10-12 hrs - the blue colour remains even when pressed

Lividity doesn’t show if the body is continual contact with something.  For example, a body lying on its back will show it in the small of the back and its neck, not parts with pressure on it, such as the back of the calf muscles and buttocks.  This feature of lividity also allows the examiner to know if the body was moved after death.

Side note:  discoloration can be different if poison was involved.  Example, carbon monoxide turns the skin cherry pink.

The above are basic ways of determining TOD.  Other ways include:  eye discoloration, food digestion, vitreous potassium, insects, plants, and putrefraction.

So, now you have more information, let’s go kill someone - in fiction only - of course!