Fingerprints and dna

The traditional approach to personal identification has been to examine an object for the presence of identifiable fingerprints, enhancing vague or partial prints as appropriate. With the advent of AFIS the next hurdle for the fingerprint examiner was to ensure that the fingerprints be of "AFIS quality." This allows the fingerprints to be entered into an AFIS and searched against the database. If the fingerprints are deemed not to be of appropriate quality, the AFIS search cannot be made. This means that the fingerprints can only be compared directly to fingerprints of known suspects, eliminating the ability to utilize the AFIS database to locate unknown suspects.

The DNA in fingerprint residues offers the potential to change all of that. Since fingerprints are partly composed of protein residues, it is possible to extract DNA from a fingerprint. The DNA may then be used to identify an individual even when the fingerprints themselves are

An off-duty federal agent was the victim of a carjacking. The carjacker disarmed the agent and turned his own gun on him. The agent was shot to death and the gun left at the scene, near his body. His vehicle, which had been stripped of its wheels and stereo, was discovered several days later near a housing project. A suspect was determined to be residing in the project.

The vehicle was carefully examined for hairs, fibers, and other trace evidence, but none was found. There were no visible fingerprints on the steering wheel, and because it had a textured surface, investigators deemed it unlikely to retain identifiable fingerprints. Furthermore, the chemicals needed to enhance the fingerprints would probably destroy any DNA that might be present. As a result, they decided to forgo fingerprinting on the steering wheel and conduct DNA testing instead.

A similar decision was made regarding the dead agent's gun, a Glock semiautomatic pistol. Its surfaces were also textured and unlikely to have identifiable fingerprints present, so investigators took swabs off the outer surfaces of the frame, slide, and trigger. Since there was no reason to suspect that the killer had handled the magazine and remaining ammunition inside, these items were not swabbed for DNA.

DNA analysis of the swabs from the gun failed to produce identifiable DNA. The swabs from the steering wheel, however, recorded DNA that was a mixture of the dead agent and the suspect. On the basis of this analysis, the suspect was convicted of the crime and sentenced to death.

Firearms, Fingerprints, and DNA

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inadequate for identification. This technology has even been applied to fingerprints lifted with tape at crime scenes: The tape has been pulled from its viewing card and the DNA extracted from the residue.

Rather than further limiting the usability of fingerprints, as AFIS has done to some degree by stepping up the quality requirements, DNA analysis works just as well on smudges and smears as on clear fingerprints. In fact, smudges and smears may be better suited to DNA analysis due to increased contact between the surface and the finger, thus resulting in the transfer of more DNA-containing material. This means that fingerprints that cannot otherwise be identified because they are smeared, incomplete, or otherwise lack adequate detail may still be useful as evidence.

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Responses

  • Jolly
    Are partial fingerprints identifiable?
    7 years ago

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