Rapid communication Development of latent fingermarks on thermal paper: Preliminary investigation into use of iodine fuming Om Prakash Jasuja *, Gagandeep Singh Department of Forensic Science, Science Block No. 1, Punjabi University, Patiala 147002, India 1. Introduction In the present era of information and technology, fast printing procedures like thermal printing are being increasingly employed. Thermal printing requires special type of thermal paper being used exclusively in the routine activities like fax machines, ATM receipts, store bills, bus tickets and in laboratory and medical instruments such as spectrophotometer, electrocardiograph, etc. Due to this high usage and handling, probability of encountering this type of paper bearing latent fingermarks as possible physical evidence has also increased. Thermal (thermosensitive) papers were introduced by National Cash Register Company in 1968 using the color forming reaction between leuco dyes and co-reactants [1]. Leuco dyes are essentially colorless solids, which forms color in presence of acidic compo- nents, electron-accepting compounds such as oxygen, iodine and heat. This reaction involves opening of the lactone ring structure that forms colored fluorane cation by extension of the conjugated double bond system. The ring opening of the lactone structure is reversible under basic conditions, which is the primary reason for the print fading on the thermal paper with the passage of time [2]. When subjected to heat, thermal papers produce black color which is indicative of the presence of unsubstituted leuco dyes while presence of substituted fluoran compounds form different color(s) such as red, green, yellow, black [3]. Development of latent fingermarks on thermal paper presents the crime scene investigators with a unique problem. Treatment with conventional techniques like ninhydrin petroleum ether or 1,8-diazafluoren-9-one (DFO), produces black color on thermo- sensitive side that conceals any fingermarks developed resulting in partial or no identification [4]. Alkyl analogues of ninhydrin soluble in the non-polar solvents have been reported to partially develop the fingermarks on the thermal paper [5,6]. Fuming of fax and thermal papers with dimethylaminocinnamaldehyde (DMAC) has also been reported to produce fluorescent fingermarks with no background coloration [7]. Treatment of thermal paper with various visualization reagents was carried out by the fingerprint and footwear forensics user group at Home Office Scientific Development Branch [8]. They concluded that pre-dipping of thermal paper in ethanol prior to processing with ninhydrin or DFO is the most effective method of preventing the blackening of thermal receipts. It is mentioned further that DFO and ninhydrin can both be used after DMAC in a sequential process. Latent fingermark development on thermal paper by metallo-porphyrin compound [(TPP) Sn (OH) 2 ] has been reported to produce better results in comparison to ninhydrin/DFO in different weather conditions [9]. Use of heptane as solvent with ninhydrin rendered Forensic Science International 192 (2009) e11–e16 ARTICLE INFO Article history: Received 5 August 2009 Accepted 5 August 2009 Available online 1 September 2009 Keywords: Personal identification Latent fingermarks Thermal paper Leuco dyes Iodine fuming ABSTRACT Thermal paper finds its extensive use in the modern day life and could act as a vital piece of physical evidence carrying latent fingermarks. A large number of citations are available in literature suggesting various techniques to develop these marks but all are suffering with one or the other drawbacks such as complex and cumbersome procedure, pre- or post-treatment, background coloration and efficiency to develop aged fingermarks. In present study, a very simple and novel method involving iodine fuming has been suggested to develop fingermarks which were not only permanent but also without any background coloration. The suggested method does not involve any pre- or post-treatment of the substrate and was able to develop very old fingermarks (upto >1 year). In this study an attempt has been made to explain the reaction mechanism of the process. In case of different types of thermal papers, presence of different substituents on leuco dye (lactone ring) structure resulted in development of different colored fingermarks upon reaction with iodine. Sebaceous material laden marks have been found to be more intensely developed as compared to eccrine marks, and the difference was more pronounced in case of aged fingermarks. ß 2009 Elsevier Ireland Ltd. All rights reserved. * Corresponding author. Tel.: +91 175 3046271; fax: +91 175 2286682/2283073. E-mail address: opjasuja@gmail.com (O.P. Jasuja). Contents lists available at ScienceDirect Forensic Science International journal homepage: www.elsevier.com/locate/forsciint 0379-0738/$ – see front matter ß 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2009.08.005