The study anticipated and was able to detect potential sources of GSR contamination in both CPD vehicles and detention facilities; however, the low numbers of unique GSR particles detected in or on potential contaminating sources suggested that the potential for secondary transfer, although possible, was relatively low. Given these findings, this study recommends that suspects be transported in marked squad cars with vinyl cloth seats and avoid transporting suspects in vehicles with cloth seats. Also, suspects should not be allowed to come in contact with table surfaces, and equipment should not be reused without some maintenance that eliminates the possibility of contamination. Suspects in shooting investigations in Chicago were routinely transported in departmental vehicles and detained in departmental facilities prior to GSR evidence collection from them. The GSR test results are used to link the suspect with primary exposure to GSR. Suspects' secondary exposure to GSR in the vehicle in which they were transported and to items in detention facilities that might have GSR previously deposited on them risk producing a false-positive GSR result for the suspect's exposure to primary GSR. Samples were collected from 193 vehicles and detention facilities. After the initial samples were analyzed, eight additional samples were taken from multiple locations in two of the facilities. Samples were collected by using scanning electron microscopy GSR kits manufactured by Tri-Tech Incorporated. The sample stubs were 1/2-inch aluminum circles covered with conductive adhesive tape. In actual casework, these stubs are used to collect evidence from the back of suspects' hands. 5 tables and 5 references