Development of Latent Fingerprints on Thermal Paper by Immersion in Hot Water.

This proof-of-concept study presents a new method of making latent fingerprints visible on thermal paper by brief ly immersing them in hot tap water. When this technique is used, a dark positive impression appears while the paper remains white and the imprint is preserved. Various factors, such as the inf luence of time since deposition and the persistence of the developed impression, were investigated. Optimal results were achieved with fresh to several hours old fingerprints. For impressions that were several weeks old, this method was not sufficiently reliable. The brightness and contrast of the developed fingerprints changed within the first week after development. The contrast of faded impressions could be increased in 75% of the samples by re-immersion in hot water. On low-sensitivity thermal papers, such as parking tickets, no fingerprints could be developed that would be sufficient for identification. Additionally, because of the need to pretest a portion of the specimen to determine the adequate developmental temperature by cutting off small paper samples, further research is needed to avoid this damaging of the evidence. [ABSTRACT FROM AUTHOR]