At the same time, it is necessary to establish the nature of the substance of the fingerprint. Is the ridge detail forming the print made in blood printed onto the surface, the blood and the print laid down in one unique event? Alternatively, is the print made in some other substance that looks like blood?
Is it a fingerprint in some other substance that has been deposited on a surface previously or subsequently contaminated with blood?
Police fingerprint experts and technicians often enhance apparent bloody fingerprints with simple protein dyes, such as amido black. One of the most common methods for discovering and collecting latent fingerprints is by dusting a smooth or nonporous surface with fingerprint powder black granular, aluminum flake, black magnetic, etc. If any prints appear, they are photographed as mentioned above and then lifted from the surface with clear adhesive tape.
The lifting tape is then placed on a latent lift card to preserve the print. However, fingerprint powders can contaminate the evidence and ruin the opportunity to perform other techniques that could turn up a hidden print or additional information. Therefore, investigators may examine the area with an alternate light source or apply cyanoacrylate super glue before using powders.
Alternate Light Source ALS : It is becoming more commonplace for investigators to examine any likely surfaces doors, doorknobs, windows, railings, etc. These are laser or LED devices that emit a particular wavelength, or spectrum, of light. Some devices have different filters to provide a variety of spectra that can be photographed or further processed with powders or dye stains.
For example, investigators may use a blue light with an orange filter to find latent prints on desks, chairs, computer equipment or other objects at the scene of a break-in. Using a fluorescent dye stain and an orange alternate light source helps this latent print appear clearly so that it can be documented. Use of various alternate light sources may help enhance the appearance of a fingerprint.
Cyanoacrylate: Investigators often perform cyanoacrylate superglue processing, or fuming, of a surface before applying powders or dye stains. This process, typically performed on non-porous surfaces, involves exposing the object to cyanoacrylate vapors. The vapors fumes will adhere to any prints present on the object allowing them to be viewed with oblique ambient light or a white light source.
A chamber specially designed for exposing latent prints to super glue fumes. Results revealed the similarity between Lac dye and Amido black on non-porous materials, in terms of both fingermark grades, and color intensity.
However, Lac dye showed relatively low performance for enhancing and developing bloody fingermarks on porous materials. This indicates that Lac dye can be beneficially used as an alternative to chemicals such as Amido black on a non-porous surface. Do not use Hungarian Red on handwriting samples, inks, hairs, fibers, and other physiological fluids that will be subsequently subjected to other forms of forensic examination.
Once fluoresced, view and photograph the evidence with orange or red barrier filters. Hungarian Red is supplied in sprayer containers. Place small objects in a suitable tray and spray the reagent onto the object from a distance of 6"-9" Allow about one minute for the dye to set. Remove any remaining water droplets with compressed air or a hair dryer set on low heat.
The surface must be completely dry before attempting to lift the developed prints using gelatin-type lifters. When examining larger objects, apply the reagent directly to the surface. Don Penven has more than 35 years direct and indirect experience in law enforcement.
He currently serves as a technical support representative and technical writer for Sirchie Finger Print Labs. He maintains the Blog: www. Printer Friendly Page. This article reviews three popular methods for blood print enhancement: Amido Black, Leuco Crystal Violet LCV and Hungarian Red Amido Black Amido black is very sensitive and works well on non-porous surfaces but its high background color light to medium blue compromises contrast on multi-colored porous surfaces.
0コメント