Laser Visualization of Bullet Paths
Written by Mark Vecellio   

The use of lasers to assist in the visualization of bullet paths is a common method used during reconstruction of shooting scenes. Bullet path analysis is essential to the full exploitation and analysis of short-range shooting scenes. It provides investigators with the flight path of the bullet, information that may help in understanding positions of shooters and victims, as well as in sequencing events.

>>See this article in its original format
in the ETM Digital Edition

At the scene, investigators usually determine the bullet path through the use of rods, probes, or strings, and sometimes with the use of mathematics. Usually, investigators will project the bullet path through space in order to help understand locations of victims and suspects, or to assist in searching for evidence. Visualization of this pathway provides context for investigators and allows a more clear understanding of the scene. In addition, within courtrooms, jurors will be able to visualize the bullet path.

There are a few documented methods of visualizing bullet paths. String is an effective method, especially during daylight hours when lasers are difficult to photograph. Lasers, however, are preferred by many reconstructionists, because strings tend to sag and create maneuverability difficulties during reconstructions. Lasers offer a few advantages over string: 1) they depict straight line visualization; 2) they offer little difficulty in maneuverability when reconstructing possible positions of shooters and victims; and 3) their projection over long distances supports thorough and precise crime scene searches for additional evidence.

The disadvantages of using red lasers are that, as noted above, they are difficult to see during bright daylight. High-wattage green lasers are available that are more visible in daylight, but they require considerable expertise in advanced photographic techniques and equipment, such as barrier or neutral-density filters. The use of green lasers on sunny days requires photographers to adjust to a parallel perspective of the trajectory, as the sunlight interferes with the laser in perpendicular perspectives. In the author’s opinion, this can be a limiting factor since parallel views make it more difficult to determine spatial relationships.

Overview of Photographic Techniques


Image 1—This photograph was taken using the water-misting method. Fill-flash was added using a flashlight. Exposure time: 13s. Aperture: f/4.5. ISO: 400.

Image 2—This photograph was taken using the card method. Fill-flash was added using a flashlight. Exposure time: 13s. Aperture: f/4.5. ISO: 400.


Image 3—This photograph was taken using the smoke-spray method. Fill flash was added using a flashlight. Exposure time: 13s. Aperture: f/4.5. ISO: 400.


Image 4—This photograph was taken using the water-misting method. Note that this scene contained a small amount of ambient light, so camera settings were adjusted until a proper amount of light was captured. No fill-flash was used. Exposure time: 6s. Aperture: f/5.6. ISO: 400.

Image 5—This photograph was taken using the smoke-spray method. Exposure time: 6s. Aperture: f/5.6. ISO: 400.

Image 6—This photograph was taken using the card method. Note the vague presence of the card on the right side of the photograph. This can be prevented by moving the card at a quicker pace and reducing the amount of light available during the exposure. Exposure time: 6s. Aperture: f/5.6. ISO: 400.

There are two traditional methods of photographing bullet paths visualized with lasers. The first method requires a person to hold a white card in the laser beam at a 45-degree angle toward the camera. In darkness, the person holding the white card will walk along the laser beam at about one foot per second, ensuring the laser beam stays in contact with the white card. After the person walks the entire length of the laser beam, fill flash can be used to provide background light, which will allow viewing of the laser-visualized bullet path, as well as the surrounding scene.

Commercially available smoke sprays are also commonly utilized to assist the visualization and subsequent photography of lasers. These sprays will allow visualization of the entire length of the laser beam and allow the photographer to photograph the beam. Then, by using fill-flash, the photographer can add whatever light is required to see the surroundings. A person simply sprays the laser beam with the smoke, nearly instantly allowing visualization of the beam. Then, the photographer exposes the photograph, being careful to manage the exposure to ensure the amount of light does not reduce the visibility of the laser light.

A more novel and inexpensive method of photographing laser light is through the use of water, sprayed in a fine mist. The water misting method is used in a similar manner as the smoke-spray method.

Note that with all photographic techniques, low light or darkness is preferred. The objective is to capture the laser beam, then add light to capture the surroundings. In most instances, the photograph should depict the laser, as well as the surrounding crime scene. If the investigator does not wish to have the surroundings present in the photograph, then simply skip the fill-flash step.

Card Method

1) Set the camera on a tripod and select the appropriate shutter speed, ISO, and F-stop, depending on light conditions and depth-of-field requirements. Note that too much ambient light could create a “ghosting” effect, in which the person walking with the card may be captured in the photograph.

2) One person will walk along the laser beam, holding the card at a 45-degree angle towards the camera, ensuring the beam strikes the card. One may choose to create a dotted laser line by simply removing the card from the laser beam for specified intervals while walking along the laser beam.

3) If warranted, fill flash can be added. Inside and smaller scenes are generally well lit through use of a flashlight. Turn the flashlight on and off rapidly. The number of depressions will depend on the scene, camera settings, and ambient light. As with all methods, some experimentation may be necessary in order to capture a sufficient amount of light, while retaining visibility of the laser.

Smoke-Spray and Water-Misting Methods

1) Set the camera on a tripod and select the appropriate shutter speed, ISO, and F-stop, depending on light conditions and depth-of-field requirements. This will generally be conducted in dark or low light conditions, thus requiring shutter speeds between five and 30 seconds. One may also choose to work using the “bulb” shutter speed.

2) One person will spray the smoke or water (tap water is effective) at the laser beam. If using water, select a spray bottle that generates a fine mist.

3) The photographer will ensure, at a given point, that the sprayer is out of view, then add fill-flash. The aforementioned flashlight method is generally effective in small, indoor scenes. The author’s crime scene investigations branch has used it effectively in 20 x 20-ft. rooms.

Advantages and Disadvantages

Card method: The primary advantage of the card method is the creation of an intense beam that is easily visible on the photograph. In addition, it is inexpensive. The primary disadvantages are a tendency to create a “ghosting effect” when too much ambient light is present, and the need to avoid obstacles at a scene that are in the pathway of the laser beam.

Smoke-spray method: Advantages of the smoke-spray method include the creation of an intense beam that is easily visible on the photograph, and the ability to easily avoid obstacles at a crime scene. One disadvantage could be the addition of the smoke to the scene. However, if this process occurs after all evidence has been collected, then that problem is eliminated.

Water-misting method: The primary advantage of using water mist is its low cost. In addition, like the use of smoke spray, one can easily avoid obstacles at a crime scene. A disadvantage of using water is that the laser beam will be less intense, when compared with the other two methods. Use of a strong laser beam or one that emits green light will mitigate this drawback. Even with a low intensity red laser light, as the photographs depict, this method does provide satisfactory results. A second disadvantage is the addition of water into the scene, but as with the use of smoke, if evidence collection has already occurred then this problem is eliminated.

So, as one can garner, visualizing laser beams during reconstruction of bullet paths has many benefits. Techniques of some methods have been presented, as have some advantages and disadvantages of each. Hopefully this information can assist you in reconstructing and documenting your next shooting scene.

About the Author

This e-mail address is being protected from spam bots, you need JavaScript enabled to view it is soon retiring from the position of Branch Chief, Crime Scene Investigations Branch, at the United States Army Military Police School at Fort Leonard Wood, Mo. He has 20 years of investigative experience, and ten years serving with the Army’s Criminal Investigation Command as a Forensic Sciences Officer. He holds a Master of Forensic Science degree from George Washington University and a Master’s in Criminal Justice from City University of Seattle.

 
< Prev   Next >






Lifting Latent Fingerprints from Difficult Surfaces

ALMOST ANYONE can find, process, and lift a latent print that happens to be in a logical and obvious place like a door handle, a beer can, or a butcher knife. But sometimes, a latent print is not just sitting there in a logical and obvious place. Sometimes, you have to use your imagination to find the print and your skills to lift it.

Read more...