In each of the previous articles that I have written I discussed both porous and nonporous surfaces and several techniques that could be used for processing these items. In this article, I would like to address the possibility of developing latent prints on surfaces that have been wet. The two general surfaces (porous/non-porous), which can be processed when they are dry, may also be processed for latent prints when they are wet.

It is not very well known that wet items can be processed for latent prints; therefore, for that very reason, most wet items are typically discounted or not submitted for laboratory processing. This article will discuss processing non-porous surfaces that are wet with Small Particle Reagent (SPR). We will look at processing wet porous surfaces in a later article.

SPR is a processing agent that comes in a liquid form and can be easily employed to process wet non-porous items for latent prints. Many of us have had the unfortunate opportunity to have to process a vehicle outside and it begins to rain. In many of these instances, getting the vehicle out of the rain is simply a futile effort. In the past, processing for latent prints on a wet vehicle had to be postponed until the surface had dried. SPR is an alternative available to us for accomplishing latent print processing while the vehicle is still wet.

Because latent prints are composed mainly of water, amino acids, oils, and a few other substances, the addition of water on the surface compounds the difficulty to develop latent prints that may be present. The majority of a latent print is simply washed away when water is applied to it. However, the oily component of a latent print is occasionally left behind even though an item may have been wet. This means that there is a possibility of developing latent prints. SPR is made up primarily of two components: Molybdenum Disulphide particles and detergent solution. The two components are mixed together to form a liquid suspension. The SPR mixture can be applied by using the submersion or spray techniques, whichever is appropriate at the time.

The submersion method is accomplished by filling the bottom of a dish (i.e. pyrex cooking dish) with the solution of SPR (Make sure that the solution has been mixed thoroughly by stirring or shaking the solution prior to use). The item to be processed can then be submerged in the solution for approximately 30 seconds to allow the solution to react with the fatty components of the latent print. The item is then removed and rinsed in the same fashion in a second dish containing clear water. During the rinsing process, be sure to gently agitate the item being processed for a few seconds. Remove the item from the rinsing solution and allow it to air dry. SPR developed latent prints are very delicate and easy to destroy and, for that reason, should be preserved as soon as possible. In some instances, SPR developed prints can be lifted, but they should be photographed on the surface before any lifting technique is attempted.

The second application method is the spray method. The spray is significantly less effective than the dish method, but this can be successful when the alternative is not available. If you are processing an item outside and it begins to rain, simply shelter the area to be processed [1]. Utilizing a pump spray bottle, shake the solution to ensure that it has been mixed well. Apply the SPR by simply spraying the surface to be processed, while still wet. When using this technique, make sure that an adequate amount of SPR has been applied to the surface. Photograph the developed latent prints as soon as possible and allow them to air dry. Photographs of the dried print should be taken again prior to lifting it.

Not only can SPR be used on wet items, but it can also be used on dry items. However, with the variety of techniques available for use on dry surfaces, a more sensitive method can generally be utilized. It should also be noted that processing with SPR is a destructive method, and will interfere with just about every other forensic examination that may be required on that item of evidence

As with any investigation, time is of the essence. Nobody wants to miss valuable evidence because they weren't aware of the possibilities for processing an item for latent prints. With technics such as SPR (and Physical Developer, which we will discuss in the next issue), we begin to see that the possibility of discovering latent print evidence is promising even in the most adverse conditions. I hope you give those techniques the opportunity to take you one step closer to solving your case.

References:
Police Scientific Development Branch, Home Office, London. "Scene of Crime Handbook Fingerprint Development Techniques," 1993, Crown Copyright, London, England, United Kingdom, pp. 75-77.

This article was reprinted in �THE PRINT� 17(6), November/December 2001, pg 7
and has been obtained from the online library provided by the
Southern California Association of Fingerprint Officers
www.scafo.org