Fingerprint Development - Powders
Fingerprint Development - Powders
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Fingerprint powder, a brush and some tape will do about 70% of the fingerprinting that is ordinarily done in crime scene processing. Powders come in all colors but normally the only two colors (really two types) are black and maybe coin box which is primarily designed for the galvanized metals of vending machine coin boxes. You can, contrary to some opinions, use black powder on black or dark surfaces and still see the prints clear enough to be lifted and placed on white cards. Use your police type high-powered flashlight if you have to.
One problem with using the lights powders like silver is that many times a the person obtaining the latent print will use the light powder, usually a gray or silver, and will then place the lifted print on either a white card or a clear hinge lifter. This yields a latent print that is just about impossible for the fingerprint examiner to see and therefore makes the whole effort futile.
Powder reacts with the oils and other foreign substances left by a person who handles a particular object. The amount of time that these oils will stay on an object depends on the surface that the print is left on as well as the surrounding environment. As an example a fingerprint left on a metal box in the room of a house will stay much longer than a fingerprint left on a box that is exposed to the outside elements of rain, dew, wind etc. There is no method to "date" fingerprints. No examiner can say that a fingerprint is "20 hours old" or "10 days" old or any other timeline. It is up to the officer to get a timeline on the print when it is needed.
How and when do you need to determine a timeline? Lets say you recover a latent print from the counter-top of a stop & rob (convenience store). One issue immediately comes into play and that is the fact that the counter top is in a place that is open to the public. To timeline this type of print you would want to find out who the last person was to clean the counter, how it was cleaned and make the determination if the print would have survived this cleaning process. This will help to create a timeline of when the print was left at a particular scene.
Obviously this is not nearly as important when you are talking about prints found at limited locations scenes. For example if you were to obtain a print from a residence, which is inherently a private location, and you identify the a latent print as belonging to Billy Burglar, then you only need to ask the homeowner if Billy Burglar has ever legitimately been in that residence. If not then the burden shifts to Billy Burglar, or his attorney, to explain the presence of that print in the residence.
One thing to note here, a fingerprint does not mean a person is guilty, only that the person had contact with a particular object or location. Once a latent fingerprint is identified the investigator should then focus on showing that there was no legitimate reason for the suspect identified to have been in a particular scene or have contact with the object from which the print was obtained.