Fingerprints have often been and still are considered one of the most valuable
types of physical evidence in identification. A complete discussion of the
history and development of fingerprints and their use in identification is
presented in Chapter 1. There are, in general, three forms of fingerprint
evidence that may be found at a crime scene: visible (or patent) prints,
impression (or plastic) prints, and latent prints. This chapter is mainly concerned
with latent prints, which, as the name suggests, are ordinarily invisible
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or less visible and thus require some means of development or enhancement
for their visualization. Over time, many investigators have explored new and
improved techniques for the development and recovery of latent prints. In
more recent years, new dimensions have been opened in latent print processing
techniques, revolutionizing the field of fingerprint identification. New
techniques have been developed not only for latent fingerprint detection, but
also for fingerprint identification. These developments have significantly
improved the efficiency of criminal investigation and personal identification.
In the past, powder dusting, ninhydrin spraying, iodine fuming, and
silver nitrate soaking were the four most commonly used techniques of latent
print development.1-4 These conventional techniques are quite effective in the
recovery of latent prints under many ordinary circumstances. However, latent
prints can be deposited on objects or surfaces with unique characteristics:
wet surfaces, surfaces with multicolored backgrounds, surfaces contaminated
with blood or other body fluids, objects with unusual shapes or contours,
waxed surfaces, fabrics or untreated wood, varnished surfaces, human skin,
cardboard boxes, and other porous or nonabsorbent surfaces. Under these
conditions, traditional methods of latent print detection are often ineffective.
At times, application of the wrong techniques may even result in the destruction
of potential latent print evidence.
For years, fingerprint scientists have sought new methods or tried to
improve existing methods for the visualization of latents. At an overall level,
all successful methods of latent print enhancement are targeted toward some
known component of latent print residue (see Chapter 3). Although a complete
understanding of all individual components in latent print residue and
their quantities has not been attained, many of the compounds present are
known. Some methods target water-soluble components while others target
lipids. The best method, then, depends on the latent, the surface, and any
environmentally induced changes. At another level, enhancement methods
exploit the chemistry of latent residue components and their potential reactions
and interactions. Efforts have focused on the development of techniques
that may be successfully applied to unique and difficult surfaces and that
offer increased sensitivity over conventional techniques. The newer procedures
can be divided into three major categories: (1) new chemical reagents
for latent print visualization; (2) optical and illumination methods for the
development or enhancement of latent prints; (3) combinations of chemical
and illumination methods. Finally, there are systematic approaches, involving
not only combinations of methods, but careful consideration of their order
of application. Some of these areas have been periodically reviewed, e.g., by
Pounds,5
Goode and Morris,6
Hazen,3
Lee and Gaensslen,7
and Lennard and
Margot.8,9 In this chapter, we discuss the various physical, chemical, and
illumination methods and systematic approaches for the enhancement and
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visualization of latent fingerprints, and also provide some of the reagent
formulations and procedures used.