Gunshot-tracking tech far from foolproof
Investigation has ID’D a number of serious flaws
CHICAGO – Michael Williams’ 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 of Cook County Jail.
His three daily calls to her had become a lifeline, but when they dwindled to two, then one, then only a few a week, the 65-year-old Williams felt he couldn’t go on. He made plans to take his life with a stash of pills he had stockpiled in his dormitory.
Williams was jailed last August, accused of killing a young man from the neighborhood who asked him for a ride during a night of unrest over police brutality in May. But the key evidence against Williams didn’t come from an eyewitness or an informant; it came from a clip of noiseless security video
showing a car driving through an intersection, and a loud bang picked up by a network of surveillance microphones. Prosecutors said technology powered by a secret algorithm that analyzed noises detected by the sensors indicated Williams shot and killed the man.
“I kept trying to figure out, how can they get away with using the technology like that against me?” said Williams, speaking publicly for the first time about his ordeal. “That’s not fair.”
Williams sat behind bars for nearly a year before a judge dismissed the case against him last month at the request of prosecutors, who said they had insufficient evidence.
Williams’ experience highlights the real-world impacts of society’s growing reliance on algorithms to help make consequential decisions about many aspects of public life. Nowhere is this more apparent than in law enforcement, which has turned to technology companies such as gunshot detection firm Shotspotter to battle crime.
The technology has been installed in about 110 American cities, large and small, including Columbus. Shotspotter evidence has increasingly been admitted in court cases around the country, now totaling some 200.
Shotspotter’s website says it is “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.
But an Associated Press investigation, based on a review of thousands of internal documents, emails, presentations and confidential contracts, along with interviews with dozens of public defenders in communities where Shotspotter has been deployed, has identified a number of serious flaws in using Shotspotter as evidentiary support for prosecutors.
AP’S investigation found the system can miss live gunfire right under its microphones, or misclassify the sounds of fireworks or cars backfiring as gunshots. Forensic reports prepared by Shotspotter’s employees have been used in court to improperly claim that a defendant shot at police, or provide questionable counts of the number of shots allegedly fired by defendants. Judges in a number of cases have thrown out the evidence.
Shotspotter’s proprietary algorithms are the company’s primary selling point, and it frequently touts the technology in marketing materials as virtually foolproof. But the company guards how its closed system works as a trade secret, a black box largely inscrutable to the public, jurors and police oversight boards.
The company’s methods for identifying gunshots aren’t always guided solely by the technology. Shotspotter employees can, and often do, change the source of sounds picked up by its sensors after listening to audio recordings, introducing the possibility of human bias into the gunshot detection algorithm. Employees
can and do modify the location or number of shots fired at the request of police, according to court records. And in the past, city dispatchers or police themselves could also make some of these changes.
Amid a nationwide debate over racial bias in policing, privacy and civil rights advocates say Shotspotter’s system and other algorithm-based technologies used to set everything from prison sentences to probation rules lack transparency and oversight and show why the criminal justice system shouldn’t outsource some of society’s weightiest decisions to computer code.
When pressed about potential errors from the company’s algorithm, Shotspotter CEO Ralph Clark declined to discuss specifics about their use of artificial intelligence, saying it’s “not really relevant.”
“The point is anything that ultimately gets produced as a gunshot has to have eyes and ears on it,” said Clark in an interview. “Human eyes and ears, OK?”
A game-changer
Police chiefs call Shotspotter a game-changer. The technology can cost up to $95,000 per square mile per year. The system is usually placed at the request of local officials in neighborhoods deemed to be the highest risk for gun violence, which are often disproportionately Black and Latino communities. Law enforcement officials say it helps get officers to crime scenes quicker and helps cash-strapped public safety agencies better deploy their resources.
“Shotspotter has turned into one of the most important cogs in our wheel of
addressing gun violence,” said Toledo Police Chief George Kral during a 2019 International Association of Chiefs of Police conference in Chicago.
Researchers who took a look at Shotspotter’s impacts in communities where it is used came to a different conclusion. One study published in April in the peer-reviewed Journal of Urban Health examined Shotspotter in 68 large, metropolitan counties from 1999 to 2016, the largest review to date. It found that the technology didn’t reduce gun violence or increase community safety.
“The evidence that we’ve produced suggests that the technology does not reduce firearm violence in the longterm, and the implementation of the technology does not lead to increased murder or weapons related arrests,” lead author Mitch Doucette said.
Shotspotter installs its acoustic sensors on buildings, telephone poles and street lights. Employees in a dark, restricted-access room study hundreds of thousands of gunfire alerts on multiple computer screens at the company’s headquarters about 35 miles south of San Francisco or a newer office in Washington, D.C.
Forensic tools such as DNA and ballistics evidence used by prosecutors have had their methodologies examined in painstaking detail for decades, but Shotspotter claims its software is proprietary and won’t release its algorithm. The company has shielded internal data and records revealing the system’s inner workings, leaving defense attorneys no way of interrogating the technology to understand the specifics of how it works.
“We have a constitutional right to
confront all witnesses and evidence against us, but in this case the Shotspotter system is the accuser, and there is no way to determine if it’s accurate, monitored, calibrated or if someone has added something,” said Katie Higgins, a defense attorney who has successfully fought Shotspotter evidence. “The most serious consequence is being convicted of a crime you didn’t commit using this as evidence.”
The Silicon Valley startup launched 25 years ago backed by venture capitalist Gary Lauder, heir to Estée Lauder’s makeup fortune. Today, the billionaire remains the company’s largest investor.
Shotspotter’s profile has grown in recent years. The U.S. government has spent more than $6.9 million on gunshot detection systems, including Shotspotter, in discretionary grants and earmarked funds, the Justice Department said in response to questions from AP. States and local governments have spent millions more, from a separate pool of federal tax dollars, to purchase the system.
Since late 2018, Columbus has paid about $2.07 million for Shotspotter, and City Council recently approved $1.13 million in spending to expand Shotspotter and renew the city’s licensing with the company for 18 months.
And amid rising homicides, this spring, the Biden administration nominated David Chipman, a former Shotspotter executive, to head the Bureau of Alcohol, Tobacco, Firearms and Explosives.
In June, President Joe Biden encouraged mayors to use American Rescue Plan funds – aimed at speeding up the
U.S. pandemic recovery – to buy gunshot detection systems, “to better see and stop gun violence in their communities.”
‘Something inside me had just died’
On a balmy Sunday evening in May 2020, Williams and his wife, Jacqueline Anderson, settled in at their apartment building on Chicago’s South Side. After Anderson fell asleep, Williams said he left the house to buy cigarettes at a gas station.
Looters had beaten him to it. Six days before in Minneapolis, George Floyd had been killed by police Officer Derek Chauvin. In Williams’ neighborhood, outrage had boiled over.
Williams found the gas station destroyed, so he said he made a U-turn to head home. Williams said Safarian Herring, a 25-year-old he said he had seen around the neighborhood, waved him down for a ride.
“I didn’t feel threatened or anything because I’ve seen him before, around. So, I said yes. And he got in the front seat, and we took off,” Williams said.
According to documents AP obtained through an open records request, Williams told police that as he approached an intersection another vehicle pulled up beside his car. A man in the front passenger seat fired a shot. The bullet missed Williams, but hit his passenger.
“It shocked me so badly, the only thing I can do was slump down in my car,” he said. As Herring bled all over the seat from wounds to the side of his head, Williams ran a red light to escape.
“I was hollering to my passenger ‘Are you OK?’” said Williams. “He didn’t respond.”
Williams drove his passenger to St. Bernard Hospital, where doctors fought to save his life. Herring was pronounced dead on June 2, 2020, at 2:53 p.m.
Three months after Herring’s death, the police showed up. Williams recalled that officers told him they wanted to take him to the station to talk and assured him he did nothing wrong.
At the police station, detectives interrogated him about the night Herring was shot, then took him to a holding cell.
“They just said that they were charging me with first-degree murder,” Williams said. “When he told me that, it was just like something in me had just died.”
“It’s not perfect”
On the night Williams stepped out for cigarettes, Shotspotter sensors triangulated a loud noise the system initially assigned to 5700 S. Lake Shore Dr. near Chicago’s historic Museum of Science and Industry alongside Lake Michigan, according to an alert the company sent to police.
That material anchored the prosecutor’s theory that Williams shot Herring inside his car, even though the case supplementary report from police did not cite a motive, nor did it mention any eyewitnesses. There was no gun found at the scene.
Prosecutors also leaned on a surveillance video viewed by AP showing that Williams’ car ran a red light, as did another car that appeared to have its windows up. This detail ruled out the possibility that the shot came from the other car’s passenger window, prosecutors said.
Chicago police did not respond to AP’S request for comment. The Cook County State’s Attorney’s Office said in a statement that after careful review prosecutors “concluded that the totality of the evidence was insufficient to meet our burden of proof,” but did not answer specific questions about the case.
As Shotspotter’s gunshot detection systems expand around the country, so has its use as forensic evidence in the courtroom – some 200 times in 20 states since 2010, with 91 of those cases in the past three years, the company said.
“Our data compiled with our expert analysis help prosecutors make convictions,” Shotspotter said a recent press release.
But even as its use has expanded in court, Shotspotter’s technology has drawn scrutiny.
For one, the algorithm that analyzes sounds to distinguish gunshots from other noises has never been peer reviewed by outside academics or experts.
“The concern about Shotspotter being used as direct evidence is that there are simply no studies out there to establish the validity or the reliability of the technology. Nothing,” said Tania Brief, a staff attorney at The Innocence Project, a nonprofit that seeks to reverse wrongful convictions.
A 2011 study commissioned by the company found that dumpsters, trucks, motorcycles, helicopters, fireworks, construction, trash pickup and church bells have all triggered false positive alerts, mistaking these sounds for gunshots. Clark said the company is constantly improving its audio classifications, but the system still logs a small percentage of false positives.
In the past, these false alerts – and lack of alerts – have prompted cities from Charlotte, North Carolina, to San Antonio, Texas, to end their Shotspotter contracts, the AP found.
In Fall River, Massachusetts, police said Shotspotter worked less than 50% of the time and missed all seven shots in a downtown murder in 2018. The results didn’t improve over time, and later that year Shotspotter turned off its system.
The public school district in Fresno, California, ended its Shotspotter contract last year, after paying $1.25 million over four years and finding it too costly.
Some courts, too, have been less than impressed with the Shotspotter system. In 2014, a judge in Richmond, California, didn’t allow Shotspotter evidence to be used during a gang murder conspiracy case, although the accused man, Todd Gillard, was still convicted of being involved in a drive-by shooting.
“The expert testimony that a gun was fired at a particular location at a given
time, based on the Shotspotter technology, is not presently admissible in court, because it has not, at this point, reached general acceptance in the relevant scientific community,” ruled Contra Costa Superior Court Judge John Kennedy.
Shotspotter says it is constantly finetuning its machine learning model to recognize what is and isn’t a gunshot sound by getting detectives and investigators to add crime scene observations to its system. As a part of that process, which they call “ground truth,” Shotspotter asks patrol officers to add and notate shell casings, bullet holes, gather witness testimony and other “evidence of gunfire” using its software.
“We have the opportunity to make the machine classification better and better and better, because we get realworld feedback loops from humans,” Clark said.
Several experts warned that training an algorithm based on a set of observations submitted by police risks contaminating the model if officers – perhaps inadvertently – feed it incomplete or incorrect data.
“I’m kind of aghast,” said Clare Garvie, a senior associate with the Center on Privacy & Technology at Georgetown Law. “You are building an inherent uncertainty into that system, and you are telling that system it’s fine. You are contaminating the reliability of your system.”
Shotspotter said the more data it receives from police, the more accurate its model becomes. The company says their system is accurate 97% of the time.
“In the small number of cases where Shotspotter is incorrect, providing feedback to the algorithm can improve accuracy,” the company said.
Beyond the Shotspotter algorithm, other questions have been raised about how the company operates. Court records show that in some cases, employees have changed sounds detected by the system to say that they are gunshots.
During 2016 testimony in a Rochester, New York, officer-involved shooting trial, Shotspotter engineer Paul Greene was pressed to explain why one of its employees reclassified sounds from a helicopter to a bullet. The reason? He said its customer, in this case the Rochester Police Department, told them to.
The defense attorney in that case was dumbfounded: “Is that something that occurs in the regular course of business at Shotspotter?” he asked.
“Yes, it is. It happens all the time,”
Greene said. “Typically, you know, we trust our law enforcement customers to be really upfront and honest with us.”
Testifying in a 2017 San Francisco murder trial, Greene gave similar testimony that an analyst had moved the location of its initial alert to a block away, suddenly matching the scene of the crime.
“It’s not perfect. The dot on the map is simply a starting point,” Greene said.
In the Williams case, evidence in pretrial hearings shows that Shotspotter initially said the noise the sensor picked up was a firecracker, a classification the company’s algorithm made with 98% confidence. But a Shotspotter employee relabeled the noise as a gunshot.
Later, Shotspotter senior technical support engineer Walter Collier – who worked for the Chicago Police Department for more than two decades before joining Shotspotter, according to his Linkedin profile – changed the reported Chicago address of the sound to the street where Williams was driving, about 1 mile away, according to court documents. Shotspotter said Collier corrected the report to match the actual location that the sensors had identified.
Law enforcement officials in Chicago continue to stand by their use of Shotspotter. Chicago’s three-year, $33 million contract, signed in 2018, makes the city Shotspotter’s largest customer.
Insufficient evidence
On July 23, Williams hobbled into Courtroom 500 leaning on his wooden cane, dressed in tan jail garb and sandals, as a sheriff’s deputy towered over him. He had been locked up for 11 months.
Williams lifted his head to the famously irascible Judge Vincent Gaughan. The 79-year-old Vietnam veteran looked back from high on his bench and told Williams his case was dismissed. The reason: insufficient evidence.
Shotspotter maintains it had warned prosecutors not to rely on its technology to detect gunshots fired inside vehicles or buildings. But the company declined to say at what point during Williams’ nearly yearlong incarceration it got in touch with prosecutors, or why it prepared a forensic report for a gunshot that allegedly was fired in Williams’ vehicle, given the fact that the system had trouble identifying gunshots in enclosed spaces.
The report itself contained contradictory information suggesting the technology did, in fact, work inside cars. Clark, the company’s CEO, declined to comment on the case, but in a follow-up statement, the company equivocated, telling AP that under “certain conditions,” the system can actually pick up gunshots inside vehicles.
Brendan Max, Williams’ attorney, said prosecutors never disclosed any of this information to him, and instead dropped charges two months after he subpoenaed Shotspotter for the company’s correspondence with state’s attorneys.
On the evening of July 23, Williams walked out of Cook County Jail into the hot Chicago night.
Williams, though, remains shaken by his ordeal. He said he doesn’t feel safe in his hometown anymore. When he walks through the neighborhood he scans for the little microphones 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?”