Exchange Principles

A vital tenet of forensic science is the exchange principle first proposed by Edmund Locard, which can be generally understood as the phrase “with contact between two items, there will be an exchange.” Every time there is a contact between individuals, environs and articles, there is an exchange of physical evidence, however small it may be. This aspect plays an indispensable role in crime scene investigations as it enables the detectives to establish links between the crime scenes, victims and the perpetrators. The imprints left behind by the friction ridge skin on the palms of hands is referred to as fingermarks. These fingermarks are instrumental in enabling identification of either the victim or the perpetrator. The detection of fingermarks …show more content…
Amino acid sensitive reagents can be used for detection of latent fingermarks only if the evidence is not wet (as water may wash away the amino acid residues). [5] The usual procedure of using amino acid sensitive reagents on evidence (porous substrates) involves dipping or spraying the items of interest with a solution of the reagent, followed by the application of heat and pressure. [1, 3] The first amino acid sensitive reagent to be used for the detection of latent fingermarks was Ninhydrin, which gave visible purple prints, due to the formation of Ruhemann’s Purple. [8] Another amino acid sensitive reagent is 1,8-Diazafluoren-9-one (DFO). A pale purple ridge pattern is visible upon the application of heat. [9] The quality of the print is thus directly related to the quantity of amino acids present. [5] All these detection techniques rely on the differences of the adherent, optical and fluorescent properties of the fingermarks and the porous substrates. …show more content…
Diane Hauze and Dr. Olga Petrovskaia, from the University of Pennsylvania (UPenn). During the evaluation of the compounds at the U.S. Secret Service (USSS) by Dr. Tony Cantu and Robert Ramotowski, it was discovered that this compound was capable of visualising latent prints. [10] Dr. Joseph Almog and researchers from the Israel National Police also synthesized and evaluated a considerable number of indandiones. [2] Australian researchers compared 1,2-indandione and 5,6-dimethoxy-1,2-indandione to ninhydrin and DFO. [11] Wiesner et al. evaluated the performance of 1,2-indandione (2 g/l in HFE-7100 solvent containing 7% ethyl acetate) on used checks. [13] These research papers concluded that indandione can visualize latent prints as well as or even better than DFO. Like DFO, the indandione do not produce strongly coloured initial print development (typically a pale pink colour), but they do produce strongly fluorescent detail when excited with green