The Chicago Police Department’s Use of ShotSpotter Technology

Pursuant to the Municipal Code of Chicago (MCC) §§ 2-56-030 and -230, the Public Safety section of the Office of Inspector General (OIG) initiated an inquiry into the Chicago Police Department’s (CPD) use of ShotSpotter acoustic gunshot detection technology and CPD’s response to ShotSpotter alert notifications. As part of this ongoing inquiry, OIG has analyzed data collected by CPD and the City of Chicago Office of Emergency Management and Communications (OEMC) regarding all ShotSpotter alert notifications that occurred between January 1, 2020 and May 31, 2021, and investigatory stops confirmed to be associated with CPD’s response to a ShotSpotter alert.

In this report, OIG details ShotSpotter’s functionality and descriptive statistics regarding law enforcement activity related to CPD’s response to ShotSpotter alerts. OIG does not issue recommendations associated with this descriptive data. OIG is issuing this analysis of the outcomes of ShotSpotter alerts to provide the public and City government officials—to the extent feasible given the quality of OEMC and CPD’s data—with clear and accurate information regarding CPD’s use of ShotSpotter technology.

The City’s three-year contract with ShotSpotter began on August 20, 2018, through August 19, 2021, at a cost of $33 million. In November 2020, well before the end of the contract term, CPD requested an extension of the contract and in December 2020, the City exercised an option to extend it, setting a new expiration date for August 19, 2023. In March 2021, CPD requested approval for an annual 5% increase in the cost per square mile of the contract.

OIG’s descriptive analysis of OEMC data and investigatory stop report (ISR) data collected for ShotSpotter alert incidents that occurred between January 1, 2020 and May 31, 2021, revealed the following:

  1. A total of 50,176 ShotSpotter alerts were confirmed as probable gunshots by ShotSpotter, issued an event number—a unique record identification number assigned to distinct “events” of police activityand dispatched by OEMC; each of these resulted in a CPD response to the location reported by the ShotSpotter application.
  2. Of the 50,176 confirmed and dispatched ShotSpotter alerts, 41,830 report a disposition—the outcome of the police response to an incident. A total of 4,556 of those 41,830 dispositions indicate that evidence of a gun-related criminal offense was found, representing 9.1% of CPD responses to ShotSpotter alerts.
  3. 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% of all CPD responses to ShotSpotter alerts. Some of those events are also among those with dispositions indicating that evidence of a gun-related criminal offense was found, where an investigatory stop might have been among the steps which developed evidence of a gun-related criminal offense.
  4. Through a separate keyword search analysis of all ISR narratives within the analysis period, OIG identified an additional 1,366 investigatory stops as potentially associated with ShotSpotter alerts whose event number did not match any of the 50,176 confirmed and dispatched ShotSpotter alerts. OIG’s review of a sample of these ISRs indicated that many of these keyword search “hits” were in narratives referring to the general volume of ShotSpotter alerts in a given area rather than a response to a specific ShotSpotter alert.

OIG concluded from its analysis that CPD responses to ShotSpotter alerts rarely produce documented evidence of a gun-related crime, investigatory stop, or recovery of a firearm. Additionally, OIG identified evidence that the introduction of ShotSpotter technology in Chicago has changed the way some CPD members perceive and interact with individuals present in areas where ShotSpotter alerts are frequent.