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What do you need to know about fingerprints?

  • Fingerprints are the most positive method of identifying someone. Even DNA cannot distinguish between identical twins, but their fingerprints are as different as any two unrelated people. The palms, soles and toes are also unique, and just as useful for identification.
  • Fingerprints are both extremely fragile and incredibly durable. They can be destroyed with a careless brush of the hand or persist for half a century.
  • Fingerprints are composed of an infinite number of potential ingredients, either naturally secreted or transferred from things we touch.
  • Different detection techniques target different specific ingredients. If the fingerprint does not contain enough of the target ingredient, the method will fail.
  • There are currently over 25 fingerprint detection techniques in common use, depending on target ingredient, composition of the substrate and condition of the substrate.
  • With expert triage, several techniques may be used successfully in sequence on the same object, revealing different impressions after different methods.
  • We do not always leave useable fingerprints for the following reasons:
    • If we have clean, dry hands (insufficient target material)
    • If our hands are dirty or we wear gloves
    • If there is not enough of the target ingredient in our sweat for the   method used.
  • There is a phenomenon called the Sympathetic Nervous System commonly known as the “Flight or Flight Syndrome”. When we are angry, fearful or nervous, changes in the body are set in motion. One of the effects is to sweat a lot more. In this condition we are a lot more likely to leave fingerprints. Criminals often do exactly that!
  • It is wrong to conclude that a person didn’t touch something, because their fingerprints were not found on it.
  • In police investigations, latent crime scene prints are compared to complete, known records of suspects’ fingerprints. This enables an expert to identify or eliminate a subject as the fingerprint source – quickly and conclusively.
  • It is more difficult when comparing latent prints to latent prints. These impressions are never complete recordings of the fingers that made them, and it is frequently impossible to determine with certainty, which finger of the hand made the impression, unless a cluster of prints is found.
  • Lastly, comparison of one latent fingerprint to another can be time-consuming and expensive. Solid strategies for acquisition will maximize chances of success.