Charles Tan: estimating time of death isn’t as simple as it sounds

On Monday evening, February 9th, police were called to the Pittsford home of the CEO of Dynamax Imaging, Liang Tan. His son Charles Tan later confessed to killing his father with several shotgun shots to the chest that evening. But the D&C is reporting that new evidence suggest that perhaps Tan’s body had laid where it was for more than a day before the police were contacted.

How can there be this much ambiguity about when Tan was shot? To most people, this would seem like the kind of thing forensic science would have down, well, cold by now. Shouldn’t such a basic fact of forensics be a quickly-determined, reliable thing?

The truth is: determining time of death is not a straightforward, formulaic process. It is a bit of an art form, requiring years of experience and careful attention to the most minute of details. And many of the clues to determining when a victim was killed are only available for a limited amount of time.

Time of Death on the Scene:

The first line of defense in a murder case is always the police on the scene. However long the body may have laid in place, the police that first arrive at the scene are the officials with the most recent contact and therefore least likely to miss evidence. Only a medical examiner (ME) or coroner can officially declare a victim dead.

Every bit of evidence is important, and nothing can be disregarded. Some of the evidence gathering would surprise some people in it’s crude methodology. One of the most basic forms of forensic evidence is to see if the victim is wearing a watch. If so, did it stop? The time on the watch offers some clues as to the time of death.

Other means of determining the time of death on scene include investigating the body for clues. The temperature of the body, it’s discoloration and the set-in of rigor mortis are all clues to the time of death. As a rule of thumb, bodies typically cool at a rate of about 1.5 degrees centigrade per hour. Rigor mortis sets in after about 12 hours. Other factors, like the amount of blood that has coagulated on the floor can also be used as clues. Here, thanks to a forensics blog, is a helpful guide to some critically-timed physiological events:

1-2 hours: ………Early signs of lividity.
2-5 hours: ………Clear signs of lividity throughout body.
5-7 hours: ………Rigor mortis begins in face.
8-12 hours: …….Rigor mortis established throughout the body, extending to arms and legs
12 hours: ……….Body has cooled to about 25°C internally.
20-24 hours: …..Body has cooled to surrounding temperature.
24 hours: ……….Rigor mortis begins to disappear from the body in  roughly the same order as it appeared.
36 hours: ……….Rigor mortis has completely disappeared.
48 hours: ……….Body discolouration shows that decomposition is beginning.

“Lividity” refers to the pooling of blood inside the body as it remains inactive and the heart stopped. As you can see, lividity – or liver mortis – is not an effective means of determining time of death past a very limited window.

In the lab, they can also test for the presence of parasitic insect larvae. After a body is completely dead, insects tend to use the body as a place to lay their eggs. An entire branch of forensic sciences is concerned solely with “forensic entomology,” or the study of the insects whose trail can be used as evidence. There are many more tests they can run in the lab, but by then, all the most immediate signs of death have long since vanished. This is why it is critical to get the evidence right on-scene.

.. But the Charles Tan Case is More Complicated:

When it comes to inspecting the body, things are dicey on-scene. That’s because the condition of the body can’t be separated from it’s circumstances. The ambient temperature of the scene, the presence of scavengers or any number of other factors all play a part in contributing to the body’s state. This winter has been one of the coldest in recent memory, and that factors into how all of these observations are interpreted. Also, because Charles Tan claimed to have killed his father that evening, it is possible that critical evidence was missed based on an assumption.

Bodies lose heat as they sit, of course. But while the rule of thumb is 1.5 degree centigrade per hour, that rule means little in especially frosty days like those we’re experiencing now. Reports so far don’t indicate where the body was found. But the shotgun was found in the garage. If he was shot in the garage and left there for a while, his body would have been a good deal colder than expected.

Even the classic sign of death – rigor mortis – is not a permanent condition. As you can see from the chart above, rigor mortis sets in within about twelve four hours after a victim has died. But it is completely gone within 36 hours. In the Tan case, that may have been the factor that threw off the initial time of death estimation – if it was assumed that Tan was shot recently then the investigators would have expected no signs of rigor mortis. And if indeed the murder took place a day before police were called, there would be no sign of rigor mortis by the time officials got to the scene.

What about insect larvae? There were not likely to be many insects in the middle of the winter. Ergo there’s not going to be a lot to go on in that sense. As I write this, no new details have been released on this case. You can expect the Medical Examiner’s Office is going over every single detail with a fine-toothed comb and inspecting the body for every last detail.

It remains to be seen exactly where and when Liang Tan lost his life and most details will never be made public. This will almost certainly include most of the forensic evidence. Whatever the truth is, it will largely be the corroboration of forensic evidence with witness statements and those of Charles Tan that will be the deciding factor.