Having received several emails with questions about the basics of how forensic scientists go about the process of examining a bite mark, it might be time for a blog on this subject. So, here we go!
About half of all bite mark cases in Tennessee involve murder victims and half are rape, child abuse, or assault and battery cases. If the victim is dead, the call is from the medical examiner’s office. If the victim is alive, the call is usually from an emergency room like Vanderbilt Children’s Hospital or an officer from the Department of Children’s Services. On rare occasions, it is a parent requesting their child to be examined from an oval injury from a day care. If the case is one child biting another, it is usually determined by the arch size. These marks are usually located any place on the child’s body where kids grab the first piece of flesh the get their teeth into.
In adult bite marks, the victim is almost always female, and her bite marks are usually located on the breast, shoulder, inner thigh or genital area.
The first step in working up a bite mark case is for the forensic scientist to determine whether or not the injury or wound is a bite mark or not. Nothing but good ol’ fashioned experience can tell you that. These wounds are oval in shape, although strangely enough, we see occasional bite marks that only involve the upper arch or lower, not both. As crazy as that sounds, it is seen. (I always wondered how it would be possible since you can’t cut paper with only one half of a pair of scissors, but no one has ever figured that part out!)
If there are two arches, the wider of the two arches is usually the upper arch and the narrower of the two would be the lower arch. This is explained by the fact that most human’s upper teeth fit over the outside of the lower teeth, and would necessitate that the upper arch be wider. One of the factors influencing whether a wound is a human bite mark would be the approximate size, since that would dictate the parameters of what a normal sized human arch would measure. Another factor would be the shape of each individual tooth print. Another factor that would differentiate a human bite from a dog bite would be the fact that a dog has three sets of incisors (front teeth) where humans have only two sets. This, plus arch size discrepancy and the dominant canine teeth with dogs would be the main factors in determining man or beast.
Once it is determined to be a human bite mark, then the next step would be to measure the tip of the canine or eye tooth to its contralateral tooth (same one on the other side). There are countless charts (not very interesting) that gives us a range of what ‘normal’ is for these dimensions. Sex cannot be determined by these measurements since a large female might measure larger than a small male.
A majority of bite marks are studied from photographs, especially if the victim is alive. It is critical that the photographs be scaled, i.e. have a ruler or some known identifiable and recognizable object in the photo. That allows us to enlarge or shrink to ‘life size or 1:1 magnification ratio’. Any photos that are not scaled are useless in study and cannot be used in courts of law. There only value would be to orient the viewer for purposes of body orientation. Many of you have seen the famous ‘ABFO #2 scaled ruler’ (pictured) which is seen on many of the CSI shows. It not only allows the photo to be scaled but also will be useful for a gray scale color correction and also the circles on the scale help to show if the image is distorted. If the circles are perfectly round, then the camera is perpendicular to the subject and has no distortion. If egg shaped or oval, then the image is distorted and cannot be trusted as admissibly reliable.
Stay tuned for our next part that focuses on Ted Bundy...
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