An investigation into effective methodologies for latent fingerprint enhancement on items recovered from fire

• We exposed prints on car rear view mirrors to fire at 300, 450 and 600 °C.
• Soot removal was carried out with three different techniques.
• Prints were enhanced using four different techniques.
• Temperature was a most significant factor: 300 °C, 92% print recovery, 450, 6% & 600, 0%.
• No statistically significant differences between soot removal & enhancement techniques.

A common assumption is that fire destroys fingerprint evidence. Recent studies have sought to challenge this assumption. This study presents a comparative evaluation of soot removal and fingerprint enhancement techniques, following fire(s) to ascertain optimal process efficacy for recovering fingerprints. Two car burns and a cremation oven were used to determine the temperature range. Temperatures of 300, 450 and 600 °C were used in simulated, controlled fires wherein cars had prints deposited on rear view mirrors. Burning occurred in a shipping container designed to approximate the variables relating to car arson. Soot removal was undertaken by tape lifting, sodium hydroxide solution, or liquid latex casting. The fingerprint enhancement techniques comprised black magnetic, aluminium and black suspension powders, or cyanoacrylate fuming with BY40 dye. A fingerprint expert classified prints as un/identifiable according to standards to be submitted as evidence in court. Multinomial logistic regression analyses were performed on the data using a p value of < 0.05 to determine statistical significance. Temperature was the biggest factor affecting fingerprint recovery. There were no statistically significant differences found between any of the soot removal methods used. Higher counts of identifiable prints were recovered with black magnetic powder and cyanoacrylate/BY40 compared to the other methods used but these findings were not statistically significant. It is recommended that recovery of fire-exposed fingerprints (which are not protected) is undertaken where suspected maximum temperatures are < 450 °C. Evaluation of optimal soot removal and fingerprint enhancement techniques should be conducted on a case by case basis.