Eli5: When examining a body with multiple possibly fatal wounds, how do you know which one killed the person?
In: Other
an autopsy report might list multiple causes of death like “stab wounds to chest and gunshot wound to leg” or they might use a generic phrase like “homicidal violence”
Wounds that occur after you die have a different structure, but if someone stabs you 10 times in the chest it’s not possible to say “Ah ha, it was stab #6.” But if they throw your stabbed body out a window, the stabs are different enough from the window cuts to know they killed you.
Most of the time it doesn’t really matter. If six people are all stabbing someone, they can all be guilty of murder, no matter which wound was actually fatal.
If it does matter (or just to learn more about wounds), they’ll examine each wound, and the crime scene, to see the blood spatter patterns, how different wounds interact with each other, and whether each wound, on its own, could have been fatal. Usually a fatal wound will bleed quite a lot, and later wounds will bleed less, because blood pressure will be lower. For example, if someone was stabbed in the heart and also had his throat slit, blood on the ceiling would indicate that the throat was cut first, and that was the wound that killed him.
The first thing is is the wound in a location and severity as to whether it could cause death by itself, then there is what happened to the wound after it was inflicted, the body reacts differently to wounds after the hearts stops pumping blood etc.
The heart pumps blood, dead people’s hearts don’t beat/pump, so initial wounds would bleed a lot and wounds with significantly less blood are postmortem.
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It’s not an exact science, but there are clues. In the case of multiple stab wounds, the medical examiner may say a few of them were potentially fatal. A stab wound would almost always cause death by bleeding, so if it didn’t injure a major vessel or the heart, it wasn’t the fatal wound. Where the blood is provides a clue. If someone had stab wounds in the carotid (neck) and aorta (chest and belly), but there’s no blood in the belly, then that stab wound happened after death. Like any other doctor, they will have info about the circumstances as well. Witnesses or details from the crime scene might also provide a clue as to what happened.
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Two separate issues here. You can tell if a wound happened before or after the heart stopped by looking at how the tissue breaks and the blood flows out because once the heart stopps the pressure drops (think of stabbing a full water balloon vs a half filled one). Also, white blood cells can’t be mobilized.
The second part comes up if two people stabbed a person simultaneously. This is where forensic specialists who understand anatomy really well. These specialists can look at the autopsy and give a very educated guess that on which stab was deadly. They will look at how fast the victim died, what organs or main arteries were hit. If one stab hit the stomach and the other the heart, if the person died immediately, we know the heart wound killed them with 100 percent certainty. In real life, there will be many shades of gray, but most testifying specialists avoid showing messy odds (doesn’t play well with juries), and express their findings as either fact and certainty or best guesses.
To give a perspective not based entirely on stabs: bruises like those that form from hanging by the neck or strangulation are also different on someone who dies from them vs someone who is hanged or strangled after death.
There are also a variety of other factors, including chemical composition (are there drugs or poisons and/or metabolites from those substances in the body?), rigor mortis, and more.
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