Blood is often found on various surfaces at crime scenes where physical violence occurred. Therefore, blood acts as a transfer medium for latent fingerprints and shoeprints. On some occasions the blood residue retains enough color and detail to permit direct photographic recovery, but generally the blood marks are too faint to permit photography using conventional light sources.

In a report published by the California Department of Justice, Bureau of Forensic Services. scientists conducted significant research indicating that certain reagents may be introduced to the visible stains or areas suspected of containing latent blood impressions.

For many years, forensic scientists have used reagents such as Leucomalachite or Ninhydrin to develop blood stains, but both of these substances have a tendency to run off or distort the prints on non-porous surfaces. On the other hand, Amido Black has proven to be quite useful.

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.

Amido Black is a protein stain, and as such should not be considered as even a presumptive test for blood, let alone a confirmatory test. The protein may be present in other body fluids, in addition to blood. However, other actual presumptive tests may be successful after the application of amido black.

The Amido Black staining solution can be methanol—or water-based. Amido Black in methanol has a greater staining power, but due to the toxicity of the methanol, it is also more dangerous. For use on a crime scene (for example, shoeprints in blood) the water-based staining solution is advised.

Leuco Crystal Violet

This reagent does not react to the normal finger constituents found in latent fingerprints like eccrine or sebaceous deposits. Rather, this reagent has an affinity for heme-based materials. When LCV and hydrogen peroxide come into contact with the hemoglobin in blood, a catalytic reaction occurs and a blue to purple/violet reaction product occurs. Leuco Crystal Violet may be used on both porous and non-porous surfaces, and may be applied with a fine mist spray or by immersing an object in the solution.

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