How can we determine if wounds with a knife were made before or after death?
If a body is found lying on the floor and there are stab wounds but very little blood, does that mean the wounds were made after death?
It is possible to determine if the stab wounds were made before a person died or after by having a looking at several things.
Stab wounds made before death are not as clean and precise as those made after death as usually the victim is moving before death and this has an effect on the way the wound looks.
The heart is beating before death and pumping blood. When the person is stabbed before death there is a lot of blood to be seen around the wound.
Another way to identify if the wound was made before or after death is to check what are called the mast cells. These contain chemicals that help in the start of the healing process and block the flow of blood. If the mast cells are degranulated it indicates the stab wound was made before death. This can be determined by taking them from the site of the wound and staining them to be viewed under a microscope.
Stab wounds are usually somewhat gaping because the knife severs the elastic tissue responsible for preserving the shape of the skin over the skeleton. There often is some subcutaneous fat bulging from the gaping wound.
If blood is circulating at the time of stabbing, the wound is antemortem, and the edges immediately under the skin have a red, hemorrhagic appearance.
By contrast, a stab wound rendered after the heart has stopped has a pale yellow color, and lacks the blood around the edges.
A third type of stab wound is termed perimortem. Here the injury occurred just before death by shock and hemorrhage. There is minimal if any hemorrhage in the wound because of the very low blood pressure due to shock and the dying process.
In the event of an overkill situation in which dozens or even 50 or more stab wounds are rendered, one will usually see a mixture of antemortem, perimortem and postmortem stab wounds. The perimortem wounds occur after the antemortem wounds, during the time when the victim is going into shock. The postmortem wounds occur after the heart stops, yet the assailant for whatever reason continues the attack.
Stab wounds during a violent altercation may have an irregular contour, perhaps showing segments with different directions as the knife goes in, then twists somewhat, then comes out. Or there may be dog-ears at the ends of the wounds, again related to twisting of the knife during the stabbing process. These irregularities indicate relative motion between the victim and the assailant. Postmortem stab wounds are less likely to have such irregular contours.
The reference is to a book by a renowned forensic pathologist by the name of Vincent DiMaio, M.D. It gives an excellent explanation of stab wounds in general, and includes descriptions of appearance and mechanisms of antemortem, perimortem and postmortem stab wounds.