Latent fingerprints are found at crime scenes much more commonly than are body fluids that contain DNA. Latent-fingerprint analysis can be useful in a wide range of crimes, including many murders, rapes, assaults, robberies, and burglaries. However, the probative value of latent fingerprints is often limited to establishing that a suspect was present at a location—and that does not automatically imply guilt. DNA analysis will be useful in more limited settings. DNA analysis will be useful primarily in rapes (because semen is often recovered) and murders (those in which either the perpetrator's blood was spilled at the crime scene or the victim's blood stained the perpetrator's personal effects—only the former will assist in identifying an unknown suspect). Where it exists, DNA evidence will often be more probative than fingerprints, in that the presence of body fluids is harder to attribute to innocuous causes. That is especially true in rape cases, in which positive identification of semen in the vagina is virtual proof of intercourse (although it leaves open the issue of whether it was consensual). Consequently, the potential utility of a DNA profile databank must be evaluated in terms of the particular crimes to which it is primarily suited.
Fingerprints have a defined physical pattern independent of the method of visualization, whereas DNA profiles are derived patterns that can be constructed with various protocols (e.g., different restriction enzymes to cut the DNA and different probes to examine different loci) that produce completely different patterns that cannot be readily interconverted. The advance of DNA technology will see the development of new protocols that offer technical advantages but produce different and incompatible patterns.
In a sense, current DNA profiles can be thought of as extremely small bits of a person's fingerprints on all or some of the fingers. Different methods look at different fingers or different locations on a finger. Only when DNA technology is capable of sequencing the entire three billion basepairs of a person's genome could a DNA pattern be considered to be as constant and complete as a fingerprint pattern. Consequently, the development of DNA databanks is tied to the standardization of methods. A national DNA profile databank can function only if participating laboratories agree on standardized methods. However, the creation of a databank with current methods could discourage the conversion to newer, cheaper, and more powerful methods.
The amount of information provided by latent fingerprints in an evidence sample is essentially fixed—it depends primarily on the portion of the finger(s) or palm found—and the forensic scientist uses all of it. DNA typing of an evidence sample yields information in an amount determined by the number of loci studied, so the forensic scientist has substantial control over the amount of information to be obtained from a sample. Conse-