When cigarette wrapping film is made of Biaxially Oriented Polypropylene (BOPP), which is colorless, transparent and very thin, the “502” fuming method, a conventional way to develop the latent fingerprint on cigarette wrapping film, is not recommended for development of fingerprint on such film because of the steadfast adherence of the fingerprint’s ingredients onto the film surface over heat, negatively affecting the following DNA examination. Hence, the optical inspection is the most preferential choice for its non-destructiveness on the latent fingerprint development. The shortwave UV reflection photography is now widely applied to develop the latent fingerprint on a variety of substrates except the BOPP film unless a modification. The colorlessness, transparency and thinness of the film are found to be the main cause. When photograph being taken, most short-wave UV lights transmitting through the film are reflected back by the object behind the film to make the lights cross the film reversely. The reflected lights are stronger than the diffuse reflection lights produced by the latent fingerprint on cigarette wrapping film, leading a failure to form an effective contrast between the substrate and fingerprint. To solve this problem, this paper proposes a modified method by utilization of some strong short-wave UV absorbing medium such as print paper, thick glass and other similar materials, to let the transmitted UV lights completely absorbed behind the film. Therefore, the lights received by the UV camera or CCD are only the left diffuse reflection lights emitted by the latent fingerprint on cigarette wrapping film. Without the disturbance of the reflected lights, the latent fingerprint on the film can be obviously distinct under shortwave UV light radiation. Whereas be cautious to the irradiation time, otherwise the over-exposure to the radiation might hinder the subsequent DNA analysis.
YANG Ming, LIU Tao.
Development of Latent Fingerprint on BOPP Cigarette Packing Film by Shortwave UV Reflection Photography. Forensic Science and Technology. 2015, 40(5): 428-430 https://doi.org/10.16467/j.1008-3650.2015.05.021