A Study of Fingerprint Development Techniques

• Main Authors: Chun-chieh Chen, 陳俊傑
• Other Authors: Sheng-Meng Wang
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/87qbpx

博士 === 中央警察大學 === 鑑識科學研究所 === 105 === There are several difficults about environment and surface limitation of development techniques. For examples, latent fingerprints develop on banknotes, bloody or wet surfaces at crime scenes. Thermal paper poses a significant challenge to latent print development as it tends to change color when traditional fingerprint development formulations are applied to it. The optimal components of ninhydrin, 1,2-indanedione (IND), 1,8-diazafluoren-9-one (DFO), and 5-methylthioninhydrin (5-MTN) for yielding clear fingerprints on thermal paper were determined by systematically adjusting the relative amounts of the reagents, polar solvents, and the nonpolar diluent petroleum ether, followed by validation on text-printed thermal paper. Specifically, 3.0% ethyl acetate as the polar solvent in petroleum ether was found to be the optimal combination; the optimal dilution ratios of ninhydrin, DFO, and 5-MTN original solutions with petroleum ether were 1 to 2, 11, and 7, respectively. The optimal concentration of 1,2-indanedione in petroleum ether was 0.125 g/L, with a string of 0.5% ethyl acetate in petroleum ether. The related factors of the vacuum instrument’s performance in developing fingerprints are also discussed, including the quantity of chemicals for vaporization, heating program arrangement, and paper of different materials. The heating program, the result indicates that under a low-vacuum condition (50 mTorr), 80–90°C is a suitable temperature range for ninhydrin vaporization. In terms of the performance on different material papers, this instrument demonstrates its capacity by developing latent fingerprints on thermal paper without discoloration or damaging the original writing, and the same results are also observed on Taiwan and United States banknotes. This study demonstrates the applications combining general fingerprint development and latent blood detection; for the porous surfaces, ninhydrin or IND were applied first for fingerprint development, then followed by leucocrystal violet (LCV) or diaminobenzidine (DAB) for blood detection. For the nonporous surfaces, cyanoacrylate ester fuming combined with dusting method were applied for acquiring latent fingerprints, then followed by individual acid yellow 7(AY7), DAB, hungarian red or luminol for blood detection. Bufferless Oil red o (ORO) was used to develop latent fingerprints on glass, transparent plastic, thermal paper, A4 paper, and Bristol boards in a wet environment. Latent fingerprints successfully developed red ridges with a pink background on thermal paper and discolored the specimen. Five rehydration solutions (ammonium hydroxide, sodium carbonate, potassium hydroxide, urea, and warm water) and three fingerprint recording methods (photograph, inking roll, and dusting tape) were investigated to process mummified fingertips from an unidentified cadaver. The results show that sodium carbonate treatment is the most effective for minutiae restoration. This study also demonstrates that even those fingertips which previously failed in urea solution, 1% potassium hydroxide solution and warm water treatment could be further improved with sodium carbonate solution to obtain qualified minutiae for fingerprint matching.