In a blistering report, the Chicago Inspector General's office calls into question the effectiveness of the police department's ShotSpotter technology.
"ShotSpotter alerts rarely produce documented evidence of a gun-related crime, investigatory stop, or recovery of a firearm," the report states. "A large percentage of ShotSpotter alerts cannot be connected to any verifiable shooting incident."
Indeed, the report's authors say that out of 50,176 ShotSpotter alerts they examined from Jan. 1, 2020, to May 31, 2021, only 41,830 led to some kind of formal disposition. And out of those, only 4,556, indicated an actual gun offense.
"We look at what we can say about how often ShotSpotter leads to the recovery of evidence of gun crime," Deputy Inspector General Deborah Witzburg told NBC 5. "And therefore, how valuable it is in combatting violent crime."
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The results seem to question that value. Out of those more than 50,000 alerts, Witzburg said her team only documented the recovery of 152 weapons.
"If the city and police department are going to continue to rely on this technology, they should be able to demonstrate its operational value," Witzburg said. "The data we examined doesn't do that."
The Chicago Police Department declined NBC 5's request for an interview. But in a written statement, the department pushed back on the report's conclusions.
"ShotSpotter has detected hundreds of shootings that would have otherwise gone unreported," the statement said. "Shotspotter is among a host of tools used by the Chicago Police Department to keep the public safe, and ultimately save lives."
CPD noted in their statement that the technology's deployment comes at a time of historically low 911 engagement.
"Law enforcement can respond more quickly to locate and aid victims, identify witnesses, and collect forensic evidence," the statement said.
That was always part of ShotSpotter's allure -- the promise that the technology would alert authorities to gunfire in virtually real time, while simultaneously pinpointing the spot where the shots were fired. But the OIG report suggested it has had a detrimental effect on policing in general.
"ShotSpotter technology in Chicago has changed the way some CPD members perceive and interact with individuals," the report states. "Some officers, at least some of the time, are relying on ShotSpotter results in the aggregate to provide an additional rationale to initiate stops or to conduct a pat down once a stop has been initiated."
It's a criticism that has been leveled in other cities where the technology is deployed.
"There's evidence that it sends police officers running into communities more often in a state of alert expecting to find a potentially dangerous situation," the ACLU's Jay Stanley told NBC 5. "And that's a potentially combustible thing."
Stanley suggested that among his organization's civil liberties concerns is that ShotSpotter employs proprietary technology which is difficult to discern.
"This is technology which is used in court to convict people and send people to jail," he said. "And if that's going to be the case, then we need to make sure that it's accurate."
CPD suggested the report was based on a mischaracterization of the way ShotSpotter is used. And that ultimately, communities victimized by gun violence benefit from its deployment.
"The system gives police the opportunity to reassure communities that law enforcement is there to serve and protect them," the CPD statement said. "And helps to build bridges with residents who wish to remain anonymous."