Gunshot Detection Systems: Considerations for Prosecutors

By Kristine Hamann,  Sophia Roach, and Sarah Solano Geisler

Overview of Gunshot Detection Systems GDS systems works by recording sounds on a network of audio sensors clustered around a designated location. The sensors transmit sound recordings, timestamps, and Global Positioning System (GPS) data to computers with proprietary algorithms that compare the input to known waveforms (graphic representations of sound) associated with the sound of gunfire. The mathematical calculations used to establish the location of gunfire are based on the same scientific principles that are used to locate the epicenter of an earthquake. Environmental factors may affect the accuracy of captured information, but modern GDS systems can detect 80% of gunfire in uncontrolled environments and pinpoint where shots were fired within as little as a 10-foot radius.2 Reliable GDS evidence has been admitted in nearly 200 cases and has established innocence, as well as guilt. GDS notifications can save lives through quicker response times and can help the police find suspects, victims, witnesses, and other evidence. Prosecutors seeking admission of GDS evidence must understand the scientific foundation of the technology, determine that it is accurate, and be prepared for legal objections. This is an evolving area where preparation by prosecutors is essential, as their work will impact the future admissibility of GDS. Information Captured in GDS Reports GDS reports generally contain information that can be used to further an investigation or as evidence in trial. This may include the date and time of the sound event, location of the sound, number of shots, and pattern of shots. An audio recording of the shots and plotting the shots on a map is usually also available. Gunshot Detection Systems as Evidence GDS recordings of live gunfire have been used as demonstrative evidence, usually through an expert witnesss in various ways including: § Connecting shooting events. § Proving the time, location, and number of shots. § Displaying characteristics of shots that provide relevant information about a firearm or use of more than one firearm. § Establishing the location of a crime scene, and, in some cases, a suspect. Considerations for Prosecutors Prosecutors should educate themselves about the many issues surrounding this evolving topic including: § How the specific technology used in their jurisdiction works. § How to preserve the data from GDS. § The standards for admissibility in the prosecutor’s jurisdiction and relevant case law, including these cases: o State v. Hill, 288 Neb. 788 (2014) o United States v. Rickmon, 952 F.3d 876, (7th Cir. 2020) o US v. Godinez, No. 19-3425, (7th Cir. 2021) o People v. Hardy, 275 Cal. Rptr. 3d 566 (Cal. Ct. App. 2021) o Wisconsin v. Nimmer, 2022 WI 47 (CASE No. 2020AP878-CR 2022) § The proprietary nature of algorithms used to interpret the data and existence of other trade secret concerns, that could affect discovery and admissibility. § The type of expert is needed to interpret the evidence at trial. § Why expert testimony may be inconsistent with automated interpretations of the data. § Criticisms of GDS technology and defense tactics to exclude GDS evidence or juror concerns about GDS evidence.  

Washington, DC: National Crime Gun Intelligence Center Initiative, 2023 17p.