Sequential Processing of Latent Prints

This article is the 11th in a comprehensive series of twelve articles on latent print development techniques written by Pat A. Wertheim. Save these issues of Minutiæ in a binder to compile a manual of fingerprint development techniques.

For many surfaces, there are several methods for developing latent prints, each of which reacts with a different component of the fingerprint residue. Frequently, it is desirable to go to extra lengths and use more than one method to locate latent prints in an important case. However, the use of one method may ruin subsequent chances of locating latent prints with other methods.

"Sequential Processing" is the use of two or more methods in a sequence designed so that each technique used avoids the destruction of fingerprint residue for subsequent methods. Two common surfaces will be discussed with a detailed sequence of several methods for each surface.

Perhaps the most common type of surface examined for latent prints is the smooth, nonporous, nonferrous surface such as glass, painted surfaces, and some hard plastics. The first step should be a close and careful visual examination of the surface for latent prints. This step could include the use of a flashlight for side lighting. It might also use the "hot breath" technique, or "huffing" to fog the surface. Any prints visually observed should be photographed before proceeding to the next step.

The second step should be an examination with a Forensic Light Source, including photography of any prints visible through inherent luminescence. Following this preliminary fluorescent examination, the surface should be "super-glue" fumed. Again, a visual examination and photography should be used before proceeding.

The next step would be to lightly dust the surface, first using nonmagnetic powder (then photographing any prints, then lifting them), followed by powdering with magnetic powder using the "hot breath" technique (then photographing any addition prints, then lifting them). Fluorescent powders may be substituted for the more traditional nonmagnetic or magnetic powders, or may be used in addition to the others.

Finally, dye staining with a suitable fluorescent dye should be done last, again followed by photography. By using all of these methods correctly and in the proper order, one could be reasonably confident of recovering any latent prints of value on the surface. Probably the second most common type of surface examined for latent prints is a porous surface such as paper or cardboard. Again, the first step should be a careful visual examination with photographs taken of any visible latent prints. Next, a fluorescent examination should be made for inherent luminescence, again accompanied by photography of any prints observed.

The next step should be iodine fuming. Although generally considered relatively unproductive, iodine fuming offers the advantage of temporarily making the prints visible without permanently altering the evidence. Any prints developed should again be photographed before proceeding. Next, magnetic powder may be used, although this is normally effective and should only be tried on very fresh latent prints. Again, prints should be photographed.

Following these methods, various liquid chemicals would be used. First, DFO would be applied, followed by a fluorescent examination and photography. Then, traditional Ninhydrin would be used, followed by photography. Finally, Physical Developer would be used. At this step, Physical Developer still frequently develops latent prints completely undetected by all of the previous methods. (The previously recommended silver nitrate method has been replaced by the more effective Physical Developer.)

Other common surface types include smooth, nonporous, ferrous surfaces; plastic films; raw wood; adhesives; waxed surfaces; and textured nonporous surfaces. For a detailed discussion of these surfaces and other less common surfaces, see the Home Office Manual of Fingerprint Development Techniques (1st edition: 1986 or 2nd edition: 1998) or the Home Office Scenes of Crime Handbook of Fingerprint Development Techniques (1st edition: 1988 or 2nd edition: 1993). For a set of simple flow charts of these methods, see Section one of the Lightning Powder Company printed product catalog.

In the next issue of Minutiæ, Pat will write about enhancement and development of latent prints in blood, the last article in the series.