Finding shell casings can be extremely difficult. A Los Angeles Police Department officer not authorized to speak to the media tells WIRED they’ve spent “hours” searching for bullet casings. Just because officers don’t find evidence of gunfire, they say, doesn’t mean it didn’t happen.

While SoundThinking says its alerts are reviewed by its Incident Review Center before being sent to the police, in Pasadena, officers who investigated ShotSpotter alerts reported that the suspected gunfire was sometimes something else entirely: a car backfiring, construction noise, or fireworks, Knock LA reported.

Chris Baumohl, an EPIC Law Fellow and coauthor of the petition to the DOJ, tells WIRED that our findings confirm what the nonprofit wrote in their petition in September: that ShotSpotter surveillance disproportionately occurs in communities of color. He also alleges that the technology primes police to go into minority communities believing that shots are fired, whether accurate or not. The result, Baumohl argues, is that community members are more likely to be picked up on bench warrants, misdemeanors, and for other reasons unrelated to guns.

In February, a leaked internal report from the State's Attorney’s Office in Illinois’ Cook County, where Chicago is located, found that nearly a third of arrests stemming from a ShotSpotter alert had nothing to do with a gun, Baumohl points out. On February 13, Chicago mayor Brandon Johnson, a vocal critic of ShotSpotter, said the city won't renew its contract with SoundThinking.

According to SoundThinking’s Chittum, the idea that police show up to ShotSpotter alerts ready to make arrests is speculation based on a few high-profile incidents. Instead, he argues that ShotSpotter provides law enforcement with accurate data to engage the community safely. “It allows police to knock on a door and tell residents, ‘Hey, we got a report of gunfire, we are just checking to see if everyone is OK. Did you hear anything? Did you see anything? If you do, please call us; we care, and we’ll come.’”

Ultimately, Chittum argues, ShotSpotter is simply a tool. When used correctly it can help police-community relations. “It’s up to the police to decide how they use it,” he says.

But what happens on the ground often paints a more complicated picture than what Chittum describes. WIRED reviewed body camera footage and police records of a 2022 ShotSpotter arrest in Cincinnati. According to the records, at 8:21 pm on New Year's Eve, police officers were dispatched to an area where two loud sounds were picked up by SoundThinking sensors. When the officers arrived, they quickly detained a tall man in a blue hoodie and black jacket who was standing near the corner where the technology had indicated gunfire.

According to police records, there were nine officers on the scene that night. Body camera footage shows one of the officers rifling through the man’s pockets as others milled around. Some pointed their flashlights at the ground or in the windows of parked cars. Others chatted, speculating about the potential whereabouts of bullet casings.

“I’m glad we could come out and help,” a sergeant watching the man being searched tells the officer standing next to him.

Police never found a bullet casing, gun, or bullet hole. They arrested the man anyway. After running his name through their on-car computer, they discovered he had warrants out for his arrest. He had failed to appear in court for traffic violations.

Additional data analysis by Matt Casey, data science content lead at Snorkel AI, a firm that helps companies with AI projects and builds custom AI with its data development platform.

Updated 2/23/2024, 12:15 pm EST to clarify that the list of sensors included in the document WIRED obtained may not include every ShotSpotter microphone.