Fingerprints can be found on practically anything. Analysts classify them into three categories according to the type of surface they were found:
1. On soft surfaces (e.g. soap, wax, wet paint, etc.) – three-dimensional plastic prints
2. Patent - visible prints are formed when blood, paint, ink, etc. is transferred from a finger to a surface, and;
3. Latent – formed when the body’s natural oils and sweats on the skin re deposited onto another surface.
How to Collect Fingerprints?
These are collected through photography. Fingerprints are photographed in high resolution with a forensic measurement scale in the image as a reference for the size. Analysts can improve the quality of the image by using low angle or alternate light source and/or chemicals or dyes for the photographs. However, in most cases, it is not necessary.
Dusting a smooth or nonporous surface with the fingerprint powder is the most common method for discovering latent prints. If any prints appear, it is photographed before it is lifted with clear adhesive tape. The tape would then be placed on a latent card in order to preserve the print. But, fingerprint powders could contaminate the evidences and ruin the examination of other prints. This is the reason why an alternate light source or apply cyanoacrylate before using powders.
Alternate Light Source (ALS)
Lasers or LED devices emit a particular wavelength or light that can be used to examine surfaces for fingerprints.
This process can be performed before applying powders or dye
stains. Usually performed on non-porous surfaces and exposing the
surfaces to cyanoacrylate vapors. These vapors will adhere to any
prints present on the object and allow them to be viewed with
oblique ambient light source.
Porous surfaces such as paper are typically processed with
chemicals to reveal fingerprints. These chemicals react with specific components of latent print residue.
Impressed prints are those that were made in soft materials or tissues by pressing down with finger or hand which can be photographed or made with molds if possible.
The Process of Fingerprint Analysis
1. Assessment of a print to determine if it can be used for a
2. Comparison of known and suspect prints
3. Evaluation of whether known and suspected prints are from the source of not.
4. Verification by another examiner to either support or refute the
conclusions of the original analyst.
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