By: Don Penven, Technical Support group
A number of special methods for development of latent fingerprints have evolved over the years. While it is not a frequent occurrence, sometimes the surface to be dusted with latent print powders is damp or wet as a result of heavy dew or precipitation.
Small Particle Reagent (SPR) was developed to handle a situation where a wet surface is encountered. SPR is formulated from finely ground chemical particles such as molybdenum disulfide or titanium dioxide mixed with a surfactant and water. A third reagent is a mixture of a fluorescent powder (that may be seen when exposed to ultraviolet (black) light, a surfactant and water.
As is the case when applying latent fingerprint development powders, either the white titanium dioxide or charcoal gray (molybdenum sulfide) is used to get the best photographic contrast. The ultraviolet reagent is indicated for use on multicolored backgrounds.
Small particle reagents are usually supplied in manual pump spray bottles. The spray is directed toward the area with the best potential for locating latent prints. On vertical surfaces the reagent is sprayed directly above the area being tested, and it is allowed to run down over this area. The reagent may also be used for tray development.
When latent prints develop—due to the reagent particles clinging to any oily fingerprint residue present—a light spray of clean water is directed toward the developed prints to wash away any excess reagent. The latents are then photographed with a scale, and then they may be “lifted” after drying.
An important feature of using Small Particle Reagent is the fact that cleanup after the prints are photographed and lifted is a matter of just wiping the surface clean with a rag or cloth. Fingerprint development powders are typically difficult to remove from many surfaces so Small Particle Reagent is an excellent alternative for outdoor use.
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References:
Crime and Clues, “Small Particle Reagent,” <http://www.crimeandclues.com/spr.htm>, April 6, 2009
Lee, Dr. Henry C. and R.E. Gaensslen ed. Advances in Fingerprint Technology, New York: Elsevier Science Publishing Co.; 1991.
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