CHICAGO (AP) — A federal lawsuit filed Thursday alleges Chicago police misused “unreliable” gunshot detection technology and failed to pursue other leads in investigating a grandfather from the city’s South Side and charging him with killing a neighbor.

Chicago prosecutors used audio picked up by a network of sensors installed by the gunshot detection company ShotSpotter as critical evidence in charging Michael Williams with murder in 2020 for allegedly shooting the man inside his car. Williams spent nearly a year in jail, and The Associated Press reported last year that a judge dismissed his case at the request of prosecutors, who said they had insufficient evidence.

The lawsuit filed by the MacArthur Justice Center at Northwestern University’s law school seeks damages from the city for mental anguish, loss of income and legal bills for the 65-year-old Williams, who said he still suffers from a tremor in his hand that developed while he was locked up. It also details the case of a second plaintiff, Daniel Ortiz, a 36-year-old father who the lawsuit alleges was arbitrarily arrested and jailed by police who were responding to a ShotSpotter alert.

The suit seeks class-action status for any Chicago resident who was stopped on the basis of the alerts. And among other things, it seeks a court order barring the technology’s use in Chicago, the nation’s third-largest city.

“Even though now I’m so-called free, I don’t think I will ever be free of the thought of what they have done and the impact that has on me now, like the shaking with my hand,” Williams said. “I constantly go back to the thought of being in that place. … I just can’t get my mind to settle down.”

ShotSpotter isn’t named as a defendant in the 103-page filing though the lawsuit claims the company’s algorithm-powered technology is flawed. The suit also alleges the city’s decision to place most of its gunshot-detection sensors in predominantly Black and Latino neighborhoods is racially discriminatory.

Messages seeking comment were left with the City of Chicago and ShotSpotter after the lawsuit was filed late Thursday morning.

ShotSpotter has vigorously defended the reliability and validity of its system, saying evidence collected by its system has been admitted in more than 200 court cases around the country. It has also pointed to an audit the company commissioned to study the effectiveness of the technology.

ShotSpotter’s website has described the company as “a leader in precision policing technology solutions” that helps stop gun violence by using sensors, algorithms and artificial intelligence to classify 14 million sounds in its proprietary database as gunshots or something else.

Those named in the lawsuit include Police Superintendent David O’Neal Brown and more than a dozen officers involved in Williams’ case, alleging they violated a host of rights guaranteed to him under Illinois law and the U.S. Constitution, including the right to due process.

Chicago police have long praised the ShotSpotter system, saying it puts officers on the scene of shootings far faster than if they wait for someone to call 911. Police have also said crime rates — not residents’ race — determine where the technology is deployed.

The filing places blame for Williams’ arrest squarely on investigating officers, who it says “put blind faith in ShotSpotter evidence they knew or should have known was unreliable” in order to charge Williams with killing 25-year-old Safarian Herring. The lawsuit alleges investigators used ShotSpotter material in a way that went beyond its intended use, quoting a disclaimer in one document related to Williams’ case that says the investigative lead summary “should only be used for initial investigative purposes.”

The AP investigation identified a number of flaws in using ShotSpotter as evidentiary support for prosecutors, and found the system can miss live gunfire right under its microphones, or misclassify the sounds of fireworks or cars backfiring as gunshots. Last year, Chicago’s nonpartisan watchdog agency concluded that actual evidence of a gun-related crime was found in about 9% of ShotSpotter alerts that were confirmed as probable gunshots.

The suit also accuses investigators of not pursuing other leads that could have produced credible suspects, including reports that someone previously shot at Herring at a bus stop.

Police and prosecutors never established a motive for Williams to have shot Herring, never found witnesses to the shooting, and never recovered a weapon or physical evidence tying Williams to the killing, the suit alleges.

“The Defendant Officers engaged in tunnel vision to target Mr. Williams, arresting him for First-Degree murder, without probable cause,” the lawsuit said.