Letter to the Editor

An argument for
photographic documentation of firearms evidence

As a forensic photographer with more than 30 years experience, I must inject some comments to some of the statements and inferences made in the article “Comparison Question” (Vol. 5 No. 6, p. 12). First, Robert J. Shem is quoted in the article: “…we work in three dimensions. The people I know who are invovled in this discipline day in and day out can make the identification on their scope, but it may not be that evident on a photograph.”

On the surface, this appears to be true. Bullets are three-dimensional. But when viewed through a comparison microscope, the image presented to the examiner is two-dimensional, not three. Actual 3D requires binocular vision. In other words, both eyes must view the object at the same time. The comparison microscope, aided by oblique lighting used to emphasize the imperfections of the bullet, presents a different image (or a composite of the two images in some microscopes) to each eye. The brain, amazing instrument that it is, interprets the 2D image as 3D—but interpretation is not reality. Therefore, the 2D image captured by a photographic device is not unlike the 2D image captured on each retina: it is 2D, not 3D.

Regarding the problem that is supposed to be related to depth-of-field, there are methods that can eliminate or avoid the problem of depth of field. One such method is by utilizing scanning photography, in which the object is moved across the field of view while being rotated, and a very thin strip of light moves along with the object as it traverses the field of image capture. This produces an image that has “depth-of-field” across the entire image that—if properly executed—contains a view as if the object were “peeled” and laid flat. Two such images, one of a “test” bullet, the other of a “suspect” bullet, can be compared side-by-side along their entire lengths, and an accurate comparison demonstrated, not only to another examiner, but to a jury. This type of scanning photography has been used in many fields, and can be traced back to Dr. Nile Root of the Rochester Institute of Technology, with additional forensic application being demonstrated by the forensic-evidence photographer, George Pearl.

Finally, I would like to point out that photographs have—if archived properly—a very long life span, over which they do not change. The human memory, on the other hand, is subject to loss, blending, and just plain error. Ten, twenty, thirty years from now, when the examiner who worked on a particular case is retired, moved away, deceased, or what have you, the photo-graphs will still be available and useable by the current examiner, even if the original evidence cannot be found.

Martin Coyne, BA, MLS, BCEP
Pittsburgh Forensics
Pittsburgh, Pennsylvania

 


ORIGINALLY PUBLISHED:
January-February 2008 (Volume 6, Number 1)
Evidence Technology Magazine
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