Estimating the Time of Death: Rigor Mortis
Rigor Mortis, like Livor Mortis or vitreous fluid, is a post-mortem change in the body that may allow investigators to establish an approximate time since death. A few hours after a person dies (and the circulatory system has stopped) the joints of the body begin to stiffen. As they stiffen they become locked into whatever position they were at the time of death (dead bodies aren’t supposed to move right?). The process is affected by temperature but as a rule of thumb for an indoor crime scene the process is noticeable after about three hours and reaches its maximum “stiffness” after about 12 hours. At this point it is very difficult to straighten the limbs and it seems as if you’d need a sledgehammer to bend them in another direction. The joint stiffness will slowly dissipate from this point leaving the body completely after about 72 hours.
One downside to the process is getting the body to fit into a standard body bag. Aside from providing another condition to estimate an approximate time since death, Rigor Mortis is also helpful in understanding the victim’s body position for crime scene reconstruction. Most people choose to avoid dead bodies unless it’s their job. So aside from first responders and the medical examiner why would someone else move a body? Of course, there is always the possibility that a family member or friend who discovers the body may try to administer some form of first aid but that isn’t too common with bodies in Rigor. Another possibility is an unscrupulous passer-by when your victim is found outdoors. Not to stereotype, but imagine a homeless person or drug addict finding the corpse of a well dressed businessman laying in the bushes of a field or something. It wouldn’t be that big a stretch for them to roll the guy and go through his pockets would it?
The last and perhaps the best possibility for your novel is having the killer come back. Returning to the scene of the crime is a high risk move but it happens. Murders are a messy and chaotic act in which your bad guy will likely be rushed. Fast forward several hours and the killer will likely be going out of his mind reliving the events (unless he’s a sociopath of course). As the killer plays the events over and over in their head they start to second guess themselves. Did I leave anything there? Will the cops believe she really shot herself? Stuff like that. For some killers the stress is unbearable and they make a decision to return and do damage control.
This is great news for CSIs and for authors because any action they take leaves more evidence for us to consider. Let’s say a victim was hit over the head with a frying pan while they laid in bed and died. Then, six hours later, the killer returns and decides that they want to stage the crime scene to look like the victim fell down the stairs and hit their head. Sounds reasonable to a dirtbag right? But when they pull the body from the bed and toss her down the stairs her body is going to be outstretched and inconsistent with what we would expect to find in an accident. Not to mention all the other evidence they will likely create in the staging process.
As an author you might consider the body position to be a key clue to discovering the place where the victim was killed. For example, maybe your victim is in a sitting position but reclined at an extreme angle. That may match the reclined driver’s seat of a car discovered in another part of town. In such a case the killer may have returned to separate the body from the car because they felt there was something about the two that would point towards the killer’s identity. There are a lot of possibilities at your fingertips so role play a bit and have some fun with it!
Posted on August 19, 2011, in The Autopsy and tagged autopsy, coroner, crime scene staging, detective, fiction, forensics, murder, police, Rigor Mortis, thriller, tom adair. Bookmark the permalink. 15 Comments.