Friday, July 17, 2020

Who gives up the most DNA?? Fingerprints or Palm Prints?

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Michael Whyte
Crime Scene Officer and Fingerprint Expert with over 12 years experience in Crime Scene Investigation and Latent Print Analysis. The opinions or assertions contained on this site are the private views of the author and are not to be construed as those of any professional organisation or policing body.
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In today’s world, fingerprints serve as one of the most fundamental and trusted means of identification. At crime scenes, specially trained crime scene examiners use a variety of techniques to develop friction ridge detail (fingerprints) so as to try and identify individuals that have been at that location. Whether it’s using conventional fingerprint powders or specialised chemical reagents, developing fingerprints that are both clear and identifiable can be somewhat difficult.

Picture perfect fingerprints (cameo’s as we call them) are rarely developed at every crime scene. A latent fingerprint is what is referred to as a ‘chance impression’, meaning that no care was taken by the individual leaving the latent impression behind. Therefore most latent prints that get developed at the crime scene are mostly partial impressions, with a highly variable degree of clarity and quality, and most of them that are developed are of no value for identification purposes.

Now before the existence of DNA testing, these low quality fingerprint impressions were discarded and not recorded in any way.  In today’s current scientific age, we can actually make use of those fingerprint smudges and it could actually offer many investigative leads that you would not have had before. DNA swabs from these low quality fingerprint impressions can actually contain enough DNA material from the skin cells sloughed off from your fingers and palms to obtain a DNA profile.

Sterile cotton tipped swab sticks

A recent article published in Science and Justice journal discusses the DNA shedding rates of the palm and fingers and provides crime scene examiners with vital information that they can take to the crime scene with them.

In the article, the researches found that the amount of DNA obtained from a palm print was significantly less than the DNA obtained from two fingerprint impressions from the same donor. What this means is that if you’re at a crime scene and you develop a smudgy palm print and a few fingers above it, which you believe are from the same hand, and say for this example you only had one swab. You are better off swabbing the finger smudges rather than the smudgy palm print in order to obtain the most DNA.

But before you start swabbing away, it is best to properly inspect the alleged smudgy fingerprint impression to see if there is any suitable friction ridge detail that could be used for a fingerprint comparison. It is common for too much fingerprint powder to be loaded onto a fingerprint brush that can then potentially ‘overload’ a fingerprint and make it appear unsuitable for a fingerprint comparison. That is why your clean-out brush is your best friend and sadly not enough people use them. A clean-out brush is a smaller version to that of the standard animal hair brush. This clean-out brush (carefully used mind you) will remove any excess powder that hasn’t adhered to the developed print and will improve the clarity of the fingerprint and hopefully provide more quality detail.

Different sized fingerprint brushes. The clean-out brush is the one with the brown handle

So if you have developed a smudgy bit of palm and some adjoining fingers and you’ve used your clean-out brush (correctly) and there’s still not enough detail there to warrant collecting it for fingerprint comparison purposes, then swab away.

So have a read of the article if you wish to get further information but hopefully what is mentioned above can give you enough information to help you next time you’re faced with this decision at the crime scene. This article will also serve as a good reference if you’re ever questioned about it in court as to why you swabbed the finger smudges rather than the palm print.

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