Friday, July 17, 2020

Recovering Bloody Fingerprints from Skin

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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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A recently published paper featured in the Journal of Forensic Identification has explored the use of a number of well-known blood developing reagents in an attempt to test the effectiveness of developing bloody fingerprints on skin, both deceased and living.

In the study, three blood developing stains were used: amido black, leucocrystal violet (LCV), and Hungarian red. The tests involved depositing varying quantities of blood from the thumb and index fingers onto human skin (both living and deceased) and testing each developing method to see which one worked the best.

  • Amido black is a chemical dye solution that binds to protein molecules in blood and produces a dark blue colour change.
  • Leucocrystal violet (LCV) reacts with the heme molecule in blood to produce a violet colour change.
  • Hungarian Red is a red chemical dye solution that binds to the protein molecules in blood and forms a bright red colour. It also has the added benefit of fluorescing when exposed to green light (515-560 nm) and a red, 600nm barrier filter attached to the lens of the camera. Requires 2% of 5-sulfosalicic acid (SSA) diluted in distilled water to be applied to the surface as a fixing agent before the Hungarian Red stain is applied.

3 reagents

Initially the authors tested the three different development reagents on a recently deceased elderly female with no refrigeration. For their subsequent tests, they focused solely on testing Hungarian Red on deceased bodies that had been exposed to refrigeration for 72 hours (3 days) and living skin using a depletion series of blood-deposited fingerprints. Their purpose on focusing on Hungarian Red was that Amido Black has already been widely used and researched over the last two decades [1] and the researchers were hoping to find a decent alternative to methanol-based amido black, because of its possible interference with toxicology results.

Based on their results, the authors reported that on freshly deceased bodies that hadn’t been exposed to refrigeration, Amido Black and Hungarian Red both tested well and developed identifiable fingerprints out of the three reagents.

Blood Reagents_Test 1

For deceased bodies that had been subjected to refrigeration, varying results were achieved however in all bodies except one, identifiable prints were able to be developed. The authors noted that “the main factor that influenced the ability to achieve good results was the actual state and condition of skin… skin from different areas of the same body, only 10 cm distance from each other, could be vastly different and could affect the ability to produce quality prints.”

On living skin, again mixed results were also observed with only a small number of prints displaying enough minutiae to be identifiable after a 60-minute post-deposit time interval. Neither the stain or fixing agent caused any irritation or pain to the person.

Living Skin

So based on the results of the paper, Hungarian Red can be employed successfully to develop bloody fingerprints on bodies, both deceased and living without the possible harmful risks associated with the methanol based amido black reagent.

An interesting area to take this research further would be test the Hungarian Red against the alternative water-based formulation of amido black discussed by Sears and Prizeman [2] in their article from the Journal of Forensic Identification in 2000. Also testing acid yellow especially on deceased persons with dark skin or bodies that have become discoloured during the different stages of the decomposition process would be interesting to see as it also possess a non-methanol based formulation. Testing these three formulations together would be an excellent target to explore for future research.

References

  1. Lawley, R. (2003), Application of Amido Black Mixture for the Development of Blood-based Fingerprints on Human Skin. J. Forensic Identification, 53 (4), 404–408.
  2. Sears, V.G. and Prizeman, T.M. (2000), Enhancement of fingerprints in blood, Part 1: the optimization of amido black, J. Forensic Identification, 50, 470–480.

Permission was granted by the authors to allow for images produced in this paper to be included in this post.

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