Fluorescent fingerprint devices.

Апр 27, 2024
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Luminescent devices for removing fingerprints

Law Enforcement Technology.- 1995 .- March.- P. 50-51.

Luminescent devices for removing Fingerprints

When the ability to detect latent fingerprints was first discovered in late 1800, the primary tool used by the investigator using this capability was a brush and a fine black powder. At the end of the 70s of our century, the same brush and powder remained the main tools for removing fingerprints. The exception was paper products that could be treated with chemicals.

In the early 1980s, research began on the use of laser radiation to detect latent fingerprints. The results of these studies have proven to be practically applicable, and various types of lasers have emerged for forensic applications. These lasers and the instruments they were used in were of great assistance to forensic scientists in detecting and recognizing fingerprints and other traces that could be used as evidence. However, they had a number of significant drawbacks: high cost, reaching up to 100 thousand dollars, large size and weight. Most of them were laboratory installations requiring powerful power supplies and water cooling systems. The output beam of laser radiation covered an area of ​​no more than 6 square cm.

In the mid-80s, more acceptable portable devices were proposed that used powerful light sources instead of lasers. In the late 80s — early 90s, industrial samples of such devices appeared, in which the luminous flux of the light source passed through light filters that formed an intense directed beam of light. This beam covered a larger area than the laser beam, which speeded up the search. Some devices had adjustable wavelength of emitted light. The cost of these portable devices was in the range of $1,000-20,000

Since 1993, two US companies have become the main suppliers of optical instruments for forensic purposes: Lynn Peavey (Blue Light device Special) and Sirchie (Blue Maxx device). In these devices, which have much in common structurally, a set of light filters is attached to the end of a standard battery-powered hand-held flashlight, for example Streamlight or Maglight. An investigator or police officer using such a device directs a beam of light onto the search area and observes objects appearing in the illuminated area through a large filter installed on a flashlight or special glasses with colored filters. Fingerprints are detected as blurry spots, which are covered with a special luminescent dye solution or black powder to process them. Particles of the solution or powder settle on the fingerprints, and when illuminated by a light source, they begin to luminesce. They can be photographed using special filters and lenses.

The most important limitation in the use of these devices is related to battery power supplies. Most flashlights with such power sources can operate continuously without recharging for 1 hour. However, in many cases, longer investigations of crime scenes or incidents are required. To overcome this limitation, it was proposed to have a sufficient number of backup devices or charged batteries in patrol cars, which is almost not always acceptable, and also to use a special power supply for the devices from a standard 120 V AC network.

Long-wave UV light sources, previously used by forensic scientists for other studies, turned out to be suitable for detecting fingerprints. The difference between such devices is that when photographing the fingerprints they detect, the use of special filters is not required. When using these UV devices, most commercially available fingerprint dye solutions and powders can be used, as well as those that cannot be used with other light sources. One of the best dye compounds for use with UV devices is the yellow-green dye «ardrox» (ardrox). After drying prints coated with a solution of this dye, they luminesce when illuminated with UV light.

Documentation of identified latent fingerprints can be done in several ways. One of them is photography. To do this, you should use reflex cameras with a lens that allows you to obtain images on a one-to-one scale. Cameras with programmable shutter speed give the best results. Depending on the clarity of the latent fingerprints, the shutter speed can range from 1 second to 1 minute or more. When using photographic slide film, negatives can be compared to black and white images. In many cases, photographed prints turn out to be more contrasty and clearer than those simply observed when illuminated by an appropriate light source.

UV devices have been used in forensic science for about 15 years. During this time, they have evolved from expensive laboratory installations to portable devices with low weight. This allows most police departments to conduct their own investigations to identify fingerprints that can be used as evidence.

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