On TV and in the movies, you've probably seen countless investigators refer with seeming accuracy to a time of death. Have you ever wondered how that is possible? Well, it turns out that investigators use what is called the Time of Death Certainty Principle -- and it's not nearly as scientific or as certain as it sounds.
It goes something like this: If you know with certainty when the person was last known to be alive, and if you know with certainty when they were found dead, then you know with 100% certainty that they died within that interval.
That is the foundation of the principle. That may seem obvious, but that is only the starting point. Once they have that interval, investigators begin to look at both medical and non-medical factors to get an approximation of the time of death.
Dr. Kiesel goes into detail:
There are changes that occur after death. Most of them are chemically related. Blood settles by gravity within the body, and there's a purple discoloration that occurs -- that's called lividity. The body will become rigid. That's called rigidity or rigor ... People have looked at vitreous humor, which is the fluid in the eye; the corneas become cloudy ... You can look at the gastric contents [food left in the stomach or intestines]. You know, when did they last eat, and that can be helpful. Do they have a full bladder or not?
All of these recognized chemical changes associated with death happen at intervals of time that are widely known. But these are not airtight indicators. Variables like ambient temperature, chemicals in the blood stream and other factors can affect the rate at which these changes occur.
Dr. Kiesel pointed out other things investigators look for when trying to establish a time of death:
Sometimes, non-medical things are more helpful to narrow the time of death. At the scene, when was the last mail that they received? The TV Guide, what page is it open to? The bottom line is: There's no one factor you can look at. There is no scientific way to determine exact time of death short of having it videotaped in front of an atomic clock.