Fingerprinting In The Lab
How are fingerprints detected at a crime scene?
At a crime scene, you could expect to find two types of fingerprints: visible and invisible. The visible fingerprints are obviously easy to detect. They are photographed and a record is made through photography, which would ultimately be brought back to the laboratory. The invisible, or latent, fingerprint is more difficult to find. It's a hidden fingerprint and it must be developed through any one of a number of means, usually through powdering or through chemicals. Once it's developed, it will be visualized and recorded and then brought back to the laboratory for further analysis.
What's the difference between a 'visible fingerprint' and a 'latent fingerprint'?
There are two types of fingerprints that we encounter. We encounter fingerprints that are visible in which you maybe touch a dirty object or a muddy object and you leave your fingerprint on the surface of something that you touch. I think we've all experienced that. The other fingerprint is what we call the latent fingerprint, which is a hidden fingerprint, which is the result of us just touching with our fingers an object, which unknown to us. There is perspiration and oils that exists on our fingers naturally that serve to transfer the image of the fingerprint onto the object that we're touching. Of course we would then have to treat that object, because we can't see it, we can't see the fingerprint because it's latent, it's hidden. So we would have to treat that latent fingerprint with powders or chemicals in order to visualize it.
How are fingerprints preserved in CSI?
What's important is the medium upon which the print is deposited, whether it's a porous medium or an un-porous medium. Because ultimately that will dictate how the fingerprint is developed. Whether it be through powder or chemical means. Once it's developed, or visualized, the print will then be photographed and the photograph will serve as the documentation of that print.
How are fingerprints identified and compared in CSI?
We know two things about fingerprints. First of all, all fingerprints come in patterns, and there are three generally recognized patterns. There are loops, swirls, and arches, but that in itself will not identify a fingerprint. What is important are the ridge characteristics that reside in the pattern, and there are numerous ridge characteristics that can be found within the fingerprint pattern, such as a bifurcation, a ridge ending, or an island. It's the number of ridge characteristics and their positions that the fingerprint examiner will look for and compare to a known fingerprint.
How are fingerprints classified in CSI?
Fingerprints come in three general patterns. All humans and all of their fingers have fingerprints that fit into one of those three categories. About 60% of the population will have loops, about 35% of the population will have whorls, and about 5% of the population will have arch patterns. So there are three general patterns to fingerprints: loops, arches, and whorls.
