Crime Scene Investigator Network Newsletter

Different formulations of white and silver powder suspensions were developed by comparing Citron detergent and Kodak Photo-Flo as the surfactant in the suspension. A mixture of both surfactants in the suspensions repeatedly produced greater fingerprint development on the adhesive side compared to using either one on its own.

Two techniques consistently performed to a higher standard for both fresh and aged marks on the adhesive side: cyanoacrylate followed by a combined basic yellow 40/basic red 28 stain and the white powder suspension. The contrast, sharpness, ridge detail, and simplicity of preparation and application achieved with both of these techniques made them superior to the other methods tested. The sequence that proved successful on the adhesive side of all tapes tested involved cyanoacrylate fuming and application of a fluorescent stain, followed by white powder suspension, and finally gentian violet with a transfer of developed marks if necessary. This sequence allowed maximum development and the greatest enhancement of latent marks, without causing the destruction of the deposit for subsequent methods. Latent fingermarks on the backing (nonadhesive side) of the electrical tape were also successfully developed with cyanoacrylate and the fluorescent stain, so treatment of the backing could be incorporated into the sequence.

Introduction
Adhesive tape can be found at crime scenes involving abductions, illicit drugs, and explosive devices. Electrical tape, in particular, is frequently used as a wrapping for drug packages, as reinforcement for the stocks of sawed-off firearms, for electrical wiring applications, or as a means to bind a victim. Amongst various types of evidence, such tapes may bear latent fingermarks on the adhesive side or on the backing.

The most well-known fingermark detection method, which has been applied successfully to the adhesive side of a variety of tapes, is the sticky-side powder method. This method involves mixing sticky-side powder with Kodak Photo-Flo and water to form a thick suspension, which is painted onto the adhesive surface using a brush and then rinsed off using water. A more recent technique is the detergent and black powder process whereby black fingerprint powder, Liqui-Nox detergent, and distilled water are combined, brushed onto the tape specimens, and then rinsed with water. A detergent, such as Liqui-Nox or Photo-Flo, is used because it contains a surfactant that reduces the surface tension of the liquid, allowing easier spreading. This means that once the powder is suspended in the liquid, the whole mixture can be applied more evenly and uniformly than if the powder was just added to water.

Similar formulations in the early stages of use include titanium dioxide (white powder) added to Photo-Flo solution, applied using a brush to the adhesive side, and then rinsed off with water, or using detergent instead of Photo-Flo. Titanium dioxide is a very fine, nontoxic, nonflammable, white powder that has not been extensively used for developing latent marks on adhesive tape, but has been proven useful for the enhancement of fingermarks on dark surfaces. It has been suggested that, when used as a substitute for sticky-side powder, titanium dioxide can produce superior results on black electrical tape and can also develop prints on both sides of the tape. The small particle reagent (SPR) technique can also develop latent marks on dark backgrounds, such as both sides of black electrical tape, by mixing molybdenum disulfide (a light grey powder) with detergent, followed by dilution with water and application as a spray.

There has been some success with fluorescent products such as Ardrox for ridge development on both sides of black tapes. This method involves mixing Ardrox with detergent and distilled water to produce a thick, milky-yellow solution. This is then painted onto the tape, rinsed off, and dried before being examined under UV light to observe fluorescence.

< read the complete article and view sample photographs. >