The City of Chicago Office of Inspector General’s (OIG) Public Safety section has issued a report on the Chicago Police Department’s (CPD) use of ShotSpotter acoustic gunshot detection technology and CPD’s response to ShotSpotter alert notifications. OIG concluded from its analysis that CPD responses to ShotSpotter alerts can seldom be shown to lead to investigatory stops which might have investigative value and rarely produce evidence of a gun-related crime.

ShotSpotter is a gunshot detection system that uses a network of acoustic sensors to identify and locate suspected gunshots, and currently operates in more than 100 U.S. cities. Chicago’s $33 million, three-year contract with ShotSpotter began on August 20, 2018; in December 2020, well before the end of the contract term, the City exercised an option to extend the contract, setting a new expiration date for August 19, 2023. OIG’s analysis of OEMC data and investigatory stop report (ISR) data revealed:

• Of the 50,176 confirmed, 41,830 report a disposition—the outcome of the police response to an incident. Of those dispositions, a total of 4,556 indicate that evidence of a gun-related criminal offense was found, representing 9.1 percent of CPD responses to ShotSpotter alerts.

• Among the 50,176 confirmed and dispatched ShotSpotter alerts, a total of 1,056 share their event number with at least one ISR, indicating that a documented investigatory stop was a direct result of a particular ShotSpotter alert. That is, at least one investigatory stop is documented under a matching event number in 2.1 percent of all CPD responses to ShotSpotter alerts.

• Through a separate keyword search analysis of all ISR narratives within the analysis period, OIG identified an additional 1,366 investigatory stops potentially associated with ShotSpotter alerts whose event number did not match any of the 50,176 confirmed and dispatched ShotSpotter alerts.

The full report can be found online at OIG’s website: bit.ly/CPDShotSpotter.