Investigation Uncovers Serious Flaws With ShotSpotter Evidence

Chicago man spent nearly a year in jail based on algorithm
By Newser Editors and Wire Services
Posted Aug 20, 2021 8:32 AM CDT
Police Jailed a Man for Murder. Algorithm Was Key Evidence
ShotSpotter equipment overlooks the intersection of South Stony Island Avenue and East 63rd Street in Chicago on Tuesday, Aug. 10, 2021.   (AP Photo/Charles Rex Arbogast)

Michael Williams was arrested last August, accused of murdering a young man from his Chicago neighborhood who asked the 65-year-old for a ride during a night of unrest in May over police brutality. The key evidence came from video of a car driving through an intersection, and a loud bang picked up by acoustic sensors. Prosecutors said audio technology powered by a secret algorithm indicated Williams shot and killed the man inside his car; Williams countered that a car had pulled up alongside his and someone shot Safarian Herring, 25. Williams was jailed for nearly a year on a charge of first-degree murder before prosecutors, citing insufficient evidence, asked a judge to dismiss the case. From the AP:

  • 'That's not fair.' "I kept trying to figure out, how can they get away with using the technology like that against me?” said Williams. "That’s not fair.” While he was in the Cook County Jail, his wife pleaded with him to remember their fishing trips with the grandchildren, how he used to braid her hair, anything to jar him back to his world outside the concrete walls, but at one point, he felt couldn’t go on and made plans to take his life with a stockpiled stash of pills.

  • The growing influence of algorithms. Williams’ experience highlights the real-world impacts of society’s growing reliance on algorithms to help make consequential decisions about public life. This is especially apparent in law enforcement, which has turned to technology like acoustic gunshot detection. One such firm, ShotSpotter, says its evidence has increasingly been admitted in courtrooms, now some 200.
  • Serious flaws exposed. ShotSpotter’s website says it’s a leader in policing technology solutions that help stop gun violence by using algorithms to classify 14 million sounds as gunshots or something else. But an AP investigation, based on thousands of internal documents, emails, and confidential contracts, along with dozens of interviews, has identified serious flaws in using ShotSpotter evidence in court.
  • Algorithms are a trade secret. AP’s investigation found the system can miss live gunfire right under its microphones, or misclassify sounds of fireworks or cars backfiring as gunshots. ShotSpotter's forensic reports have been used in court to improperly claim that a defendant shot at police, or provide questionable counts of the number of shots fired. It calls the technology virtually foolproof, but its algorithms are a trade secret, largely inscrutable to the public, jurors, and police oversight boards.
  • How it works. The company identifies possible gunshots with the acoustic sensors. Then ShotSpotter employees listen to audio recordings of those sounds, and confirm or change the source of sounds, introducing the possibility of human bias. Employees can and do modify the location or number of shots fired at the request of police, according to court records.
  • The Williams case. Evidence in pre-trial hearings shows ShotSpotter first said the noise the sensor picked up was a firecracker but a ShotSpotter employee relabeled it a gunshot. Later, a ShotSpotter engineer changed the reported Chicago address of the sound to the street where Williams was driving, about a mile away, court documents show. ShotSpotter said the report was corrected to match the actual location that the sensors had identified. ShotSpotter insists it warned prosecutors not to rely on its technology to detect gunshots inside vehicles or buildings.
  • Williams remains shaken. When he walks through the neighborhood, he scans for the acoustic sensors that almost sent him to prison for life. “The only places these devices are installed are in poor Black communities, nowhere else,” he said. “How many of us will end up in this same situation?"
(More algorithms stories.)

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