Tuesday, November 24, 2020

A burglary by the sea… How to successfully develop fingerprints exposed to sea spray

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Michael Whyte
Crime Scene Officer and Fingerprint Expert with over 7 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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There are a number of fingerprint development techniques that can be used to develop and enhance latent fingerprints on a variety of surfaces, whether it be porous, non-porous, or semi-porous surfaces. Often, a crime scene examiner will encounter difficult surfaces such as the adhesive side of tape, items that are wet, objects exposed to extreme temperatures, or objects covered in snow.

Searching through the vast array of online resources, journals, and books you will find numerous methods, chemicals, or special powder formulations to combat these difficult surface types. A particular difficult surface type often encountered by crime scene examiners but has received little research, are surfaces exposed to sea spray, or more specifically, sea spray aerosol.

In a recent study published in Forensic Science International, researchers have narrowed down and identified the best developing methods for the examiner to use when they come across sea spray affected surfaces. These surfaces often appear tarnished with a white coloured haze from the evaporated sea water and are difficult to obtain identifiable fingerprints from.

The study has only focused on glass surfaces so it will be interesting to see whether all the methods suggested work just as well on all non-porous surfaces.

For surfaces that have received less than 1 week exposure to sea spray, results of the study showed that dry fingerprint powders performed in the range of 89–53% of returned identifiable prints with magnetic white and standard white performing the best (89% and 78%, respectively). This indicates that 1 week’s exposure is not long enough to fully degrade the eccrine and/or sebaceous constituents. So if you’re lucky to come across a crime scene where the occupants of the premises have cleaned the windows recently, you should have a good chance of developing identifiable fingerprints with either standard white or magnetic white fingerprint powder.

For surfaces that have received up to a month’s exposure to sea spray, the study found that standard fingerprint powders (including magnetic) were terrible at developing any identifiable prints (< 3%). What they found however was that powder suspensions methods, such as white sticky-side powder, were the most effective. Iron (III) oxide suspension was reported to achieve the highest success rate (67%).

Wetwop™ Black and White Fingerprint Suspensions

This is great news for examiners, lucky enough to be operating on the coastline, because it provides an alternative method to experiment with. It would be common place to expect that most windows examined fitting this scenario, would have been exposed to sea spray for greater than a week. Examiners can now add sticky-side powder such as Wetwop™ White to their arsenal of developing products since they would already be using it in the fingerprint laboratory.

It must be noted that the use of any suspension powder can be somewhat messy and consent from the home owner would definitely have to be obtained prior to use. Careful examination of the target area would have to be carried out to identify the best areas to apply the suspension powder rather than just painting the entire surface. This would not be very cost effective because the suspension containers are relatively small and one container may only be enough to cover one large window. So for minor category crime scenes such as burglary or break and enter offences, testing a small area around the point of entry, such as shards of glass from a broken window or frame, would be best practice. For major crime scene categories such as home invasions, sexual assaults, and murders then a larger area can be targeted.

IMPORTANT NOTEBefore trying out the use of the powder suspension in the field, please ensure that you have permission from both your law agency (to use it) and home owner (to apply it on their stuff). Also, make sure that you’re confident in the application of suspension powders and that current standard operating procedures (SOPS) exist in your workplace for application and adequate cleanup procedures.

If examiners found success from these techniques listed in the study or have other techniques that have worked well, feel free to share them as a comment below.

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