The pathologist is often asked to give an opinion as to the characteristics of a knife used in a killing. Was the knife single- or double-edged? What was the length of the knife blade? The width? Was the blade serrated? Was more than one knife used?
One should be extremely cautious in giving answers to these questions. In most cases, on examining a wound, the most information that can be deduced is the maximum width of the blade, an approximation of the length of the blade, and whether it is single-edged. If the stab wound passes at an oblique or perpendicular angle to Langer's lines, one must reorient the wound edges to see the true appearance of the blade.
One can never definitely link a knife to a wound unless the tip of the knife has imbedded itself in the body and broken off (Figure 7.14). If the knife is recovered, this tip can be matched to the knife by tool mark comparison. A physical match in such a case is as valid as a ballistics match of a bullet.
In most instances, the most that one can do when presented with a knife and asked if it was the weapon that produced a specific wound is state that it could have been. To be sure that a knife blade was serrated from the appearance of the wound is rare (Figure 7.15).
All knives thought to have injured or killed an individual should be examined for the presence of blood or tissue. Any blood or tissue present can be typed by DNA techniques so as to link the weapon to the victim. It is possible for a knife or similar weapon to not show microscopic blood staining after it has been used to stab an individual. In stab wounds of solid organs, bleeding occurs only after the knife is withdrawn because pressure of the knife in situ prevents bleeding. During withdrawal of the knife, the muscular and elastic tissue of the solid organs stabbed or the elastic tissue of the skin may contract about the knife and wipe off the blood present on the blade of the knife. During its withdrawal from the body, the knife may also be wiped clean by the clothing. If a knife appears to be free of blood, the handles should be removed to see if any blood is there. With folding knives, the recess for the blade should also be tested for blood. Even though the blade or recess may appear to be free of blood or tissue, analysis of wipings of the blade might still yield sufficient tissue to perform at least limited DNA analysis and typing. This may be sufficient to link a weapon to a victim.
On rare occasions, a knife is found embedded in the body. To remove it, the thumb and index finger should grasp the sides of the handle immediately adjacent to the skin. This will enable the examiner to avoid touching that portion of the knife handle that was in contact with the assailant's hand, where fingerprints may have been left.
Rarely, the weapon is found firmly clenched in the deceased's hand (Figure 2.4). Cadaveric spasm, an intense muscular contraction of the hand, which occurs at the moment of death, provides unequivocal proof that the person had the weapon in his hand prior to death.
Usually, following a suicidal stabbing, the weapon is found immediately adjacent to or a short distance from the body. Absence of blood on the hand is inconsistent with a suicidal cutting of the throat, but may occur with suicidal stab wounds of the chest or abdomen. The absence of a weapon at the scene of a death suggests a homicide because an assailant usually does not leave the weapon at the scene of death. Rarely, a suicide victim survives
long enough to clean the weapon and replace it in its usual storage area or hide it. It is also possible for a perpetrator to leave the weapon near the body to suggest a suicide.
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