Sharp force injuries (or injuries produced by objects with sharp edges) are divided into three different categories: stab wounds, incised wounds, and chop wounds. Each injury and its location should be analyzed. For instance, most homicidal stab wounds are frontal and on the left side of the body, as most people are right handed.
When trying to determine whether the wound was caused from a single-edged knife, a double-edged knife, or a serrated knife, the size and shape of the wound must be closely analyzed. For instance, a single-edged knife causes a regular, linear wound without abraded margins. A single-edged blade will also one blunt end and one pointed end, hence the term “single-edged.” Likewise, a double-edged knife will cause an oval-shaped wound, with both margins of the external skin appearing in a V-shape. A serrated-knife (knife with teeth) may cause serration marks, such as ragged-edges around the wound with more damage to the surrounding tissue.
Determining the type of Sharp force injury can be very tricky, for a number of reasons, when it comes to investigations. For instance serrated knives are usually indistinguishable from wounds caused by single-edged knives. The body and skin, being pliable, can stretch and distort the wound, dependent upon the angle, force, and so on from which the knife was applied. The presence of “bridging tissue” in the depth of the wound, below the skin surface usually indicates a laceration (tearing apart of tissues; a type of blunt force injury), which should be distinguished from a sharp force injury. This does not occur with sharp force injuries, as these sharp objects result in the separation of surrounding tissue.
The technical meaning of a stab wound is a wound made by a sharp object in which the depth of penetration into the body is greater than the length of the wound on the skin. The opposite is true for an incised wound (shown above), where the length of the injury on the surface of the skin is less than the depth of penetration. The same knife can be used to create both types of wounds. For instance, an attacker could swing a sharp knife at a victim, and the knife could penetrate the skin slightly causing a longer wound than deep cut. In this instance, the tip of the knife will cause all of the damage. On the other hand, the attacker could use that same knife and thrust it deep into the victim, causing a typical type stab wound.
Cast-off splatter can also tell investigators several things about how the crime took place. For example, if the splatter was found on the walls and on the ceiling, it could indicate that the attacker swung the knife back or raised the knife forcefully, several times, away from the victim and back into the victim. This would cause the blood to fly off the knife, as it is being swung away from the victim, and deposit onto the walls and ceiling—likely on the walls behind the attacker or on the ceiling at a 90-degree impact angle. As the instrument continues to swing backward, the movement accelerates and additional blood will “cast-off” the knife, approximating a linear pattern.