Statistics show that the first 24 hours is the most critical time in the investigation of a crime scene. For investigators who are working crimes that involve firearms, the ability to quickly, accurately, and inexpensively detect whether potential suspects have recently discharged, handled, or were in close proximity when a firearm was discharged is of paramount importance. In 2002, the Sandia National Laboratories developed a portable field-test gunshot residue (GSR) kit that provides an immediate indication of recent gun use and allows investigators to rapidly focus on prime suspects at or near the crime scene. The kit is available to law enforcement agencies under the name of Instant Shooter Identification Kit (ISID-1), available from Law Enforcement Technologies, Inc. The kit is a binary test; it offers the user the ability to perform two completely different tests relating to gun use. It provides a fast, on-the-spot field-screening method, known as presumptive testing, for nitrocellulose that indicates whether or not the suspect has recently been exposed to an environment in which a firearm was recently discharged. Second, and more importantly, the field-test results can subsequently be confirmed by the more conventional scanning electron microscope (SEM) testing process in the laboratory, known as evidentiary testing that can be used at time of trial. To date, testing of ISID-1 by Sandia Laboratories has shown 90 percent accuracy relating to false positives and 89 percent accuracy relating to false negatives for the field portion of the kit, and 100 percent correlation between the field data and the lab data. A controlled study on the reliability of the lab portion is ongoing. The benefits of ISID-1 are that it is inexpensive, simple, requires minimal training, and can be easily configured for field use. Users of the kit have reported several different scenarios for using the kit. It can be used to collect evidence from suspects; it can be used to help distinguish between suicide and homicide cases by testing the victim and all suspects for GSR; and it can be used to help reconstruct crime scenes.