The ShotSpotter system and the value of diverse juror perspectives
Erik Loomis points to this AP story on ShotSpotter, a system that police and prosecutors use to identify gunshots, react to potential crimes, and prosecute suspects. The AP story raises serious questions about the accuracy and integrity of the system. You can click through for their story, which is gripping and definitely worth a read.
The ShotSpotter story reminded me of an experience I had as a juror several years ago. The charges in the case were pretty straightforward. Four college kids were walking home from a bus terminal when they were approached from behind by three men. There was a loud bang that the victims interpreted as a gunshot. They turned around, their assailants said they were armed and robbed them. The cops quickly found the suspects, including the one who was on trial.
The evidence was fairly compelling, and we eventually convicted the defendant, but there were also problems with the evidence and we took three or four days to reach a verdict. One problem was that the most important charge was armed robbery, but no gun was found. The victims thought they had heard a gunshot and a ShotSpotter system had recorded a gunshot. But the incident had happened at a bus depot, and there was some chance the “gunshot” had been the sound of a bus backfiring. There was some testimony about the ShotSpotter system; I don’t remember the details, but it amounted to little more than “trust me”.
We were having a not-so-interesting and not-so-well-informed discussion of the chance that the noise the victims heard could have been a bus rather than a gun, when a young black guy on the jury spoke up. He said, more or less, the following: “My friends and I were standing in front of a bus at xxxx (another bus depot) and the bus backfired. We thought it was a gunshot, so we ran. There were some cops across the street. They thought it was a gunshot and that we had fired it, so they started chasing us.”
Now, if I remember correctly, he (the young black guy) still thought it was likely they had heard a gunshot. Still, it was a remarkable example of the value of diverse perspectives. It would have been easy for a jury of middle class white folks who don’t take the bus, don’t worry much about gunshots, and don’t get chased by cops to just assume that it’s easy to distinguish a bus backfiring from a gunshot, or to assume that buses don’t backfire that often, etc.
Eric:
Everything is up for grabs in the courts. If the truth gets out in the open without doubt being cast by attorneys, you are fortunate.
You were also fortunate to have someone who experienced similar with busses and could explain how the police reacted to him. When I think of a pistol or rifle shot, I recall sounds which were different than those of backfiring busses or cars. Backfires can be mistaken for gun shots if you have never fired a weapon or have had little exposure. I would not be sold-on the sound being from a gunshot.
Even so, they did threaten the other people. Prison, not likely, other alternatives. Enough black men in prison.
The last time I was on a jury, the police and prosecutor claimed probable cause to search a vehicle because the driver turned right at a corner, then immediately turned right into the gas station on that corner. The driver claimed that on turning the corner, they could see that the price of gas at a station down the street was higher, so they turned into the station.
We ended up believing the driver, especially as the price of gas was over $4 a gal at the time in our area.
Backfiring in newer internal combustion engines is quite rare. You could sit in a bus terminal listening for months, even years without hearing one, unless the bus company was running a bunch of really old busses. Even so, I presume that ShotSpotter really ought to have spectral analysis capability to further assist identifying sounds.
Eric: You “presume that ShotSpotter really ought to have spectral analysis capability” but there is no reason to believe that it does, or if it does that they utilize the data properly. As the AP article linked above says:
“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.”
And as studies by National Academy of Sciences and other organizations have shown, most “forensic science” is crap.
Bob:
Thank you for the explanation