Crime Scene Investigator Network Newsletter

Introduction
How far away from the actual bullet strike can a string reconstruction be accurately performed? One of the largest limitations of the string method is the effect of gravity on the string. This is readily apparent to anyone who has attempted this type of shooting reconstruction. The nylon string that is typically used for this type of reconstruction sags lower and lower the farther you get from the impact point, causing the investigator to wonder just how accurately the string approximates the flight of the bullet. This article is an attempt to answer this question.

A typical way to perform a string reconstruction is to place a dowel rod or commercially designed probe through a set of holes that are left as a bullet passes through the drywall on both sides of a wall. The rod is then secured in place, protruding at least a foot or so on the side where the reconstruction is performed. The string is attached to the base of the rod near the wall so that the direction of the string can be compared to the protruding rod as the alignment is adjusted. If the bullet strike is lower on the wall, I prefer to attach the string so that it runs along the top of the rod. This way, a glance from above can confirm alignment of the horizontal aspect of the angle. At close ranges of less than ten to fifteen feet or so, the vertical alignment is performed by pinching the string between the thumb and index finger and aligning the string with the rod while sighting back down the string. Unfortunately, this alignment method does not work farther away because it is hard to see the small diameter of the rod and to tell whether the string is aligned closely. The string can be aligned from farther distances by starting the adjustment process with the string held up too high and then slowly lowering it until the string just meets the tip of the rod. This is accomplished by either attaching the string to a tripod to allow for fine adjustment as you walk back and forth to do the comparison or by using an assistant to watch and give instructions while you adjust the termination point of the string. The obvious question is, How far is too far?

The method of reconstruction by trigonometric calculation can provide a baseline to compare string reconstruction data if performed simultaneously. The calculation method uses the horizontal and vertical aspects of the impact angle and basic trigonometric formulas to project the flight path away from the strike in a linear fashion. Although a bullet does not travel in a straight line, this method can provide a very close approximation of the flight path.

Method
A practice wall made of typical 2" x 4" framing and drywall, with a number of pre-existing, full-penetration, 9 mm bullet strikes, was used. It has a pair of wooden legs that can be swiveled to allow for the adjustment of the vertical angle of the wall.

This wall was placed on a level concrete floor and a wooden dowel rod was placed through one of the bullet holes. The rod was secured in place and then a nylon string was attached for the string reconstruction. The string was stretched tightly to a distance of ten feet and was then attached to a camera tripod at a height that an average person might hold a handgun (Figure 1). The angle of the wall was then adjusted to get the rod close to the angle of the string. The fine adjustments of the string were then made using the controls on the tripod. The height of the string at ten feet was then recorded. The angle of the rod was calculated with a digital level and angle finder. The height of the

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