The enhancement of latent fingerprints from human skin continues to be a problem for forensic laboratories. Pig skin is closely related to human skin in thickness, basal cell density, collagen fibers, vascular supply,¹ subcutaneous fat, sweat glands, color, and hair follicles.² Therefore pig skin was an ideal model for this study because of its accepted resemblance to human skin.³ Previously it was believed that latent fingerprints were recoverable for up to a few days,⁴ and in some instances up to two months on human skin.⁵ This article presents a procedure to recover three month old latent fingerprints from pig skin.

Skin was isolated from a fresh pig carcass. Using a scalpel, a section of full thickness skin was removed from the muscle tissue and then cut into five cm² pieces. The skin samples were either frozen (-20°C) or refrigerated (4°C) until needed. When the experiment was performed, the skin section to be tested was removed from its preservation temperature and permitted to come to room temperature. This allowed excess moisture to evaporate from the skin surface. A fingerprint was prepared by rubbing the thumb from a designated researcher onto their own forehead. The thumb was then placed on the skin samples using the amount of force one would associate with an attacker, and saved over a predetermined length of time. Predetermined lengths of time consisted of 3, 5, 7, and 9 days as well as a two week period, and finally three months. The skin was suspended from clips in a 40 liter laboratory cyanoacrylate fuming chamber which was placed inside a vented fuming hood. A small heater (VWR Scientific model 210 hotplate325 Watts) was placed inside the chamber. A small amount (2g) of cyanoacrylate was added and heated to completion of volatilization. Cyanoacrylate fumes were allowed to volatilize for an additional ten minutes. The skin was removed from the chamber and immediately sprayed with a stock solution of Ardrox® Fluorescent Dye (Faurot® L-7067, Elmsford, NY). Contrary to Faurot® instructions, the best results were obtained when the sprayed skin was allowed to air dry for 60 seconds prior to rinsing with purified water. Pink or black magnetic fingerprint powder was added to the skin and it was immediately taken to a dark room and exposed to a 365 nm UV light source. Photographs were taken in a dark room while the print was still exposed to UV light, with a fixed lens digital Olympus camera, using a macro setting. The photographs were taken from a distance of 10-12 cm, while a 10X optical magnifying glass was held in frontof the lens.

The skin yielded excellent fingerprints with clear ridge details. The use of fluorescent pink and black magnetic fingerprint powder assisted in enhancing fingerprints for photographic preservation. The results were consistent for latent fingerprints as old as three months. Figure 1 shows a three month old latent fingerprint detected by this method and enhanced with fluorescent pink fingerprint powder.