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Crime-Fighting Laser Beams

The result is an incredibly high-contrast image that clearly shows the fluorescing evidence, not the background. I've never experienced anything like it.

In 2000 I was lucky enough to tour the United States Secret Service headquarters in Washington, D.C., and I found its forensic laboratory particularly impressive. The Secret Service is renowned for having some of the best fingerprint technicians in the world, with a state-of-the-art fingerprint laboratory to match. I saw technology I'd only read about up to that point. One instrument that caught my eye was a massive two-meter-long Argon-Ion laser.

This laser was on an eight-foot-long optics table. Large tubing snaked across the table to supply the required liquid cooling of this power-hungry laser. The cost of such a device? As the saying goes, if you have to ask…. But according to the technicians, this laser allowed evidence processing that no other forensic light source technology could match.

Obviously, these devices were only used by the largest agencies because of their cost and size. Times have changed. Today Coherent Inc. offers a state-of-the-art fully portable forensic laser light source for under $50,000. Still a large sum of money, but much more accessible to a larger number of agencies.

Forensic Light Source Basics

A forensic or alternate light source is a device that outputs a specific wavelength or color of light. Many light sources are capable of outputting many different wavelengths of light, from ultra-violet, through the visible spectrum and into the infrared region. Some materials fluoresce when this colored (or UV or IR) light is applied. Biological fluids (semen, urine, saliva, vaginal fluid, blood, etc.), fingerprints, hairs/fibers, bone fragments, and chemical accelerants are just an example of the many types of evidence that can be located using forensic light sources. Each particular type of evidence responds best to a specific wavelength of light. Generally speaking, the range from ultraviolet light to green light is the most useful for locating evidence and processing fingerprints. In order to see the evidence, all light sources are used with barrier filters—goggles and/or photographic filters. The barrier filter blocks the colored light from the forensic light source but allows the light from the fluorescing evidence to pass through so it's visible.

Many different forensic light source technologies exist, including laser-based systems, lamp-based systems, and LED- (light emitting diode) based systems. All of these different technologies have their strengths and weaknesses. In my experience, most law enforcement agencies around the country that utilize forensic light sources are using a xenon lamp-based system. These include Spex CrimeScopes, Rofin Polilights, and the OmniPrint from OmniChrome. Smaller handheld LED light sources are becoming more popular because of their low cost and high portability. I have personal experience with lamp and LED forensic light sources, but I had never had the opportunity to use a laser light source until earlier this year when Coherent delivered a TracER for evaluation.

Coherent and the TracER

Santa Clara, Calif.-based Coherent  Inc. is a world leader in laser technology. In 1997 Coherent introduced one of the first semi-portable forensic laser light sources. This device, named the Incriminator, weighed over 100 pounds and cost well over $100,000. But it was a milestone product because this multi-watt solid state laser could be taken from the laboratory into the field for use at crime scenes. The Incriminator required access to a 110-volt AC power supply and a large dolly with wheels to transport it around the scene.

Like all technology, laser technology has made steady improvements in miniaturization and portability. In 2005 Coherent introduced the TracER forensic laser light source. TracER stands for Trace Evidence Recovery. This diode-based solid state laser provides a whopping 5 watts of power output in a completely self-contained portable light source. The TracER is marketed as weighing less than 50 pounds and costing under $50,000. At close to 50 pounds the TracER is certainly not light, but this weight includes its built-in DC (direct current) power supply and battery. That's right, the TracER is unique because it can be powered from a standard 110-volt AC outlet or it can run off of its integrated battery for about 1.5 hours of continuous use. This means no more portable generators and extension cords in your remote crime scenes.

Physically, the TracER is about the size of a large breadbox. It has a carrying handle on top and a 15-foot fiber optic cable that delivers the laser light. This cable terminates in a hand wand that allows the user to adjust the spread of the laser with an optical zoom, as well as control the light intensity. The TracER outputs a fixed wavelength of light at 532 nanometers in the green spectrum.

Laser light is completely different from other types of light sources. A laser provides a coherent beam of monochromatic light. Comparing the light output of a laser light source to a lamp-based light source is like comparing apples and oranges. A 5-watt laser is far brighter and more powerful than a 1,000-watt lamp-based light source. According to Coherent, a 1,000-watt lamp-based light source is only producing less than 1 watt of light energy at the end of the wand because the light is incoherent and much of the light is lost through filters and as heat. In contrast, a 5-watt laser produces a full 5 watts of output power without the light leakage of other designs.

My Experiences

I spent about a week with the TracER earlier this year. I used it both in the laboratory and in the field. Let me say this, I have never seen a more powerful light source in operation. The 5 watts of green laser light made our 500-watt xenon lamp system look dim by comparison. In the lab I used the TracER to illuminate fingerprint evidence that I had processed with various chemical dyes and stains. I felt that the TracER consistently showed me more ridge detail than either lamp or LED forensic light sources. Because the green laser light is pure, there is no light leakage through the barrier filter, which can obscure the evidence. The result is an incredibly high-contrast image that clearly shows the fluorescing evidence, not the background. I've never experienced anything like it.

This made not only fingerprint evidence easier to photograph, but all types of evidence. I found that I was using much shorter exposure times when using the TracER. Shorter exposure times can equate to better photographs, especially when using digital cameras. This is because digital cameras generally exhibit more digital noise at longer shutter speeds.

I used the TracER at a sexual assault scene where the assault occurred on both the bed and on the sofa. Operating the TracER on cordless battery power, I put on my orange barrier goggles and began to examine the scene. Potential biological evidence leapt out at me. The TracER's high-power output allowed me to scan larger areas of the scene in far less time than with smaller handheld light sources. Power is really one of the main advantages of a larger forensic light source like the TracER. It's convenient to carry a small handheld LED device, but that means you're searching the scene in square inches, instead of square feet or even square yards.

The TracER in Use

I spoke with Kenneth Jones, a forensic specialist with the San Luis Obispo (Calif.) Sheriff's Department, an agency that serves a population of about 250,000. The agency purchased a TracER about a year ago. According to Jones, one of the main benefits of the TracER is the ability to use the device without an AC power source. He gave an example of processing an old house without power in a very rural area. Instead of powering up a generator and running extension cords through the scene, Jones and his team were able to fully process the scene using the TracER's internal battery. Jones said this was a big selling point to his supervisors when deciding to purchase the TracER.

The San Luis Obispo SD uses the TracER in both the laboratory and, because of its portability, in the field. According to Jones, the agency has had excellent success with the TracER in the field locating trace and biological evidence as well as locating accelerants remaining at arson scenes.

Jones says his agency has had great success with the TracER in the fingerprint laboratory. The San Luis Obispo SD often processes fingerprint evidence with dye stains and fluorescent powders. Jones feels that the higher intensity of the TracER often shows more fingerprint ridge detail than other light source technologies.

At one crime scene he observed an inherently luminescent fingerprint with the TracER. This was the first time he had ever seen this phenomenon. The fingerprint was on a terra cotta clay pot. Jones was examining the pot before carrying out further fingerprint development. When illuminated with the TracER, this fingerprint was visible with no other processing. Jones was able to photograph the fingerprint, enter the print into AFIS, and make a match to the suspect.

San Luis Obispo SD uses the TracER in conjunction with other forensic light sources, including the xenon lamp-based OmniChrome. Jones feels it's useful to still have light sources that offer tunable wavelengths of light, including ultraviolet light and blue light. He believes the TracER is an excellent addition to his toolbox and it's helped his agency solve cases. That's what it's all about.

The Coherent TracER is a unique forensic laser light source that offers cutting- edge technology with incredible power and portability. It's already in service with the FBI, the Bureau of Alcohol Tobacco and Firearms, and the Border Patrol, as well as many smaller agencies throughout the United States, Canada, and the United Kingdom.

While not a replacement for all other forensic light sources, the TracER absolutely excels in trace evidence and fingerprint processing and imaging. It's hard to convey the power of this laser light source. With a competitive price point and unique features it might be time for your agency to consider adding a TracER to your forensic tool kit.

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David Spraggs is an investigator and firearms instructor with the Boulder (Colo.) Police Department. He teaches forensic photography and crime scene investigation, is a frequent contributor to POLICE, and serves as a member of the POLICE Advisory Board.

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