A trace of evidence

New material aids investigators in lifting trace evidence

     If too much material is applied to a surface, the polyvinylsiloxane may run down past the fingerprint. In this case, the investigator can simply place a piece of tape a few inches below the print to create a dam. The tape will allow the excess material to gather in this area. After AccuTrans dries, users can cut off the excess with a pair of scissors or a knife.

AccuTrans to the test

     Researchers recently devised a comparison test using various substrates to determine the ways in which AccuTrans might be used. They applied the product to each substrate, and the drying time was noted for every surface. After the material cured, the impressions were lifted and compared for quality, and to determine whether the latent fingerprint needed to be reversed.

     All latent fingerprint impressions produced in the study were photographed on a light table for maximum results and clarity, and scaled 1:1. Researchers used a Nikon D100 Digital Camera, set on ISO 1000 in Aperture Priority Mode at f/16, equipped with a Sigma 50mm Macro Lens.

     The tests were conducted with Accutrans transparent and brown casting material using the following surfaces.

     Rough surfaces:

  • Golf ball
  • Concrete block
  • Bricks
  • Rocks
  • Fruits (lemon, lime, orange)
  • Computer surfaces
  • Dashboards
  • Unfinished wood

     Smooth surfaces:

  • Dollar bill
  • Light bulbs
  • Glass
  • Mirrors
  • Finished wood
  • Smith & Wesson 9mm handgun
  • Wesson 9mm slip

     Special surfaces:

  • Dry blood prints
  • Human skin
  • Fingers and palms

     The brown AccuTrans casting material was tested on the following toolmarks:

  • Hammer hit in wood
  • Pry marks on screwdriver
  • Smith & Wesson 9mm handgun barrel

     The examinations considered ease of mix and application, drying time, latent quality, and latent reversal requirements.

     The rough surfaces tested revealed that latent fingerprint impressions on all of the substrates, except the concrete block, yielded positive results and latent fingerprints of value. The concrete block displayed what appeared to be finger marks, and when AccuTrans was applied and the prints lifted, the finger marks contained little ridge detail. All lifted latents were of AFIS quality, except for those on the concrete block. The product's drying time was approximately 3 minutes at 78 degrees F. Researchers determined back light photography may be needed if the AccuTrans becomes too thick for AFIS entry or comparison. (See Figure 2 of a latent lifted from a lime and Figure 2A of a latent print from a vehicle dashboard on Page 86.)

     The smooth surfaces were found to provide an excellent area from which to lift latent fingerprints, furnishing positive results and latent fingerprints of value on all of the substrates tested. In fact, all of the latents lifted were of AFIS quality. Due to the use of the AccuTrans transparent, the latent prints were ready to be added to AFIS immediately. As was the case with rough surfaces, back light photography may be needed if the AccuTrans becomes too thick for AFIS entry or comparison. In this test, latents did not need to be reversed. The product's drying time was approximately 3 minutes at 78 degrees F. (See Figure 3 on Page 86 to view a latent print lifted from a light bulb.)

     The special surfaces test allowed researchers to experiment a bit with AccuTrans in order to recover fingerprints from human skin and dried blood, and actual finger and palm impressions. The finger and palm impressions were of excellent quality and easily comparable. On deceased persons, it was determined that AccuTrans can be used to assist in identification by casting the decedent's fingerprint impressions. Doing this is fairly simple: When the material is dry, a small amount of release agent is applied to the inside of the cast and the cast is then filled with AccuTrans and allowed to dry. After drying, the impression can be rolled on a fingerprint card for identification purposes. Another method would be to dust the fingers with magnetic powder, apply transparent AccuTrans to the deceased's fingers, allowing the material to dry, then removing the impressions from the fingers. Back light photography would then be used for comparison purposes, producing a positive print.

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