OUTLIERS MEDICAL-FORENSIC FILES: Knife Wound Analysis by DP Lyle, MD

OUTLIERS MEDICAL-FORENSIC FILES: Knife Wound Analysis by DP Lyle, MD

Can the ME Determine the Type of Knife Used in a Murder By Examining the Wounds?

Q: I am writing a story about a killer who uses a specific knife and kills the same way every time. The knife is unique in that it has a long blade that is serrated on one side, curvy on the other. I'm trying to determine if the wound can be used to identify at least some aspects of the knife.

Her method of kill is to plunge the knife into the abdomen, just below the sternum, then to pull the handle towards herself and push the blade up and to the right in an attempt to puncture the heart. She twists the knife as she pushes it upward in an attempt the conceal details about the knife, mainly the fact that the blade is serrated on one side.

Would it be possible to ascertain from the wound that there are serrations on the knife, perhaps that the blade is curvy, that the tip of the knife curves and that there is some kind of decoration on the guard?

A: The problem with wound analysis here is that with the movements of the blade, the internal slashing that you describe, the wound would be significantly distorted. This would make the ME’s job very difficult.

When the medical examiner examines a stab wound with an eye toward determining the type of weapon used, he will measure the length and width of the blade and the depth of the wound. It is sometimes possible to determine whether a blade was single-edged or double-edged, and if serrated one side. It requires a fairly clean in and out stab wound if he is to have any hope of accomplishing this. Any movement of the blade muddies the water. This could be from the victim struggling to get away or it could be from the attacker using the knife in a manner similar to what you describe. I should point out that the depth of the wound would only determine the minimum length of the blade. It could be longer but it could not be shorter and make such a wound.

That said, there still are a few things that might help you. Even with the internal slashing motion, the medical examiner might be able to determine that one edge of the blade was serrated by examining the skin around the entry wound. This might or might not be possible but at least it's not impossible. Also, if the knife is driven to the hilt, then the hand guard could cause bruises or abrasions of the skin around the entry wound. If so, this would indicate that the depth of the wound is the actual length of the blade. Also, the shape and any pattern on the hand guard might imprint on the skin as bruises or abrasions. This might also help identify the type of weapon used. If a suspect weapon is recovered, the medical examiner should be able to say that the victim's wound is consistent with the suspect weapon. Simply from the physical nature of the wound, he could not say it was exactly that knife, only that it was similar and consistent with the murder weapon.

There is one other thing that might help you. Blood invariably gets on the blade, the hand guard, and even the handle with such injuries. Obviously, the killer would clean the knife, but blood might seep into the gap where the hand guard and the blade or the blade and the hand guard join. It can also settle into the nooks and crannies of the handle itself. Sometimes even cleaning the knife will not eliminate these hidden sources of blood. If the medical examiner located this and obtained a usable sample, he could create a DNA profile of the blood. If this then matched the victim's DNA profile, he would know that this knife, to the exclusion of all others, was the murder weapon.

Lastly, even with knives that possess hand guards, the attacker will often suffer hand and finger cuts as the knife slips in his hand. Leaving his blood on or around the victim can prove he was present, and that would require some explaining.

DP Lyle MD

https://www.dplylemd.com/