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As much as it could help police, ShotSpotter’s not ready for the courtroom

Accused individuals have a constitutional right to confront their accusers. They can’t cross-examine ShotSpotter.

ShotSpotter equipment overlooks the intersection of South Stony Island Avenue and East 63rd Street in Chicago on Aug. 10.
Charles Rex Arbogast/AP

Authorities should be wary of using ShotSpotter, a detection system that alerts police to gunshots, as the heart of criminal cases against individuals.

Police use bloodhounds to help find evidence at crime scenes, but Illinois courts don’t allow handlers to interpret what the dogs were thinking on the scene. Similarly, ShotSpotter is useful when it quickly directs police to gunfire, but using it in court as definitive evidence of where a shot was fired raises red flags.

Accused individuals have a constitutional right to cross-examine their accusers. But, just as with bloodhounds, they can’t cross-examine ShotSpotter or do their own analysis of its data. ShotSpotter’s forensic analysts submit a report based on a deeper dive into data gathered by the surveillance equipment, but the company that owns ShotSpotter keeps its algorithm secret.

A Chicago man, Michael Williams, was in jail for almost a year after prosecutors based a murder case against him on data from ShotSpotter. In July, a judge dismissed the case after prosecutors said they had insufficient evidence. The case against him had rested on video of a car driving through an intersection and data from ShotSpotter that pinpointed that as the spot where a gun was fired in the car. ShotSpotter says it told prosecutors its evidence was not sufficient to support the theory of the crime because its system does not work indoors, including inside a car.

ShotSpotter can turn up useful evidence if police arriving on a scene find witnesses or shell casings, even if the shooting has stopped before they get there and the shooters are gone. Police say ShotSpotter is often on target. But until independent, peer-reviewed double-blind studies confirm the accuracy of ShotSpotter, its ability to pinpoint exactly where a shot took place is not irrefutable evidence that should be the foundation of a criminal court case. Yet ShotSpotter evidence has been admitted in about 200 court cases in 20 states.

ShotSpotter says it provides an important service because 80% to 90% of the time residents don’t bother to report gunfire, which normalizes gunplay on the streets, while SpotSpotter flags almost 100%. But ShotSpotter is unpopular among activists who say it is inaccurate and that money spent on the alarm system could be used in more productive ways. On Thursday, activists in Englewood protested against the city’s decision to extend its $33 million ShotSpotter contract for two years.

The late University of Illinois Chicago School of Law professor Melvin Lewis used to say that too often the only standard courts set for forensic evidence was that it be incriminating to the defendant. We need a higher standard for ShotSpotter.

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