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Monday, November 4, 2013

ShotSpotter Detection System

The Washington Post has an article praising the ShotSpotter detection system used by Washington D.C. law enforcement. The article describes the system:

About 39,000 separate incidents of gunfire have been documented by ShotSpotter’s unseen web of at least 300 acoustic sensors across 20 square miles of the city, according to an analysis by The Washington Post. The data, obtained through a public-records request, offer an unprecedented view of gun crime in a city where shooting a firearm is illegal in virtually all circumstances.
The gunfire logged by ShotSpotter overshadows the number of officially reported felony gun crimes by more than 2 to 1. More than one-half of the incidents detected by the network have involved multiple rounds of gunfire. In 2009 alone, ShotSpotter captured more than 9,000 incidents of gunfire. That number has fallen by 40 percent in recent years as gun homicides have declined sharply.


... The network covers only a third of the city, focusing on the police districts with the most violent crime. It occasionally misses gunfire because of circumstances that can cloak acoustic signatures, such as the canyonlike structures of an urban landscape. Some sounds, such as fireworks, can be mistaken for gunfire, although technology and human review help weed out false positives.
When ShotSpotter’s remote monitors — microphones and circuitry in a weatherproof shell — detect a loud noise, a central computer program analyzes the acoustic signature, providing a more accurate location than people usually can. It classifies the source, pinpoints the suspected location to within a few yards and notifies police. City personnel verify the alert and dispatch officers.


“ShotSpotter gives you a specific location,” said Kristopher Baumann, president of the D.C. police union. “You can go there and get out of the car. You can find a victim or shell casings.”
 The article indicates that the City initial installation of sensors cost $2 million, and that the City has spent an additional $3.5 million over the past six years maintain and expand the system. So what has the City received for this money? Who knows--the City told the Washington Post that "they do not track arrests made as a result of ShotSpotter’s alerts," and the information is not frequently used at trials. In fact, the article can only point to two cases where it made any difference--it helped provide a defense for an off-duty officer sued for wrongfully shooting a teenager (although the City still settled the claim), and:

Prosecutors said the technology helped win a voluntary manslaughter conviction in the slaying of 20-year-old Deuante Ray in the early morning of Oct. 30, 2009. Prosecutors called it a “difficult circumstantial evidence case.”
A gunman shot Ray in the head and chest, killing him in an alley behind the 1100 block of 48th Street NE. A witness last saw Ray entering the alley that night with Terrell Patton. Patton denied shooting Ray but admitted that he lent Ray his cellphone.

Records showed that two calls were made from the phone that night. The second call by Ray, to his girlfriend, ended about 12:35 a.m. ShotSpotter detected a gunshot in the alley about 15 seconds after the call ended. That, prosecutors said, was one of the shots that killed Ray. Patton, they said, lured Ray into the alley and shot him.
“Technology provided key evidence,” prosecutors noted.
So, we are faced with a choice of either (a) incompetent tracking and spending of money because the City isn't collecting data to evaluate its effectiveness, or (b) notwithstanding it has detected 39,000 shots, it has only helped with prosecution of a single case. Basically, the only result is that it shows that D.C.'s gun laws are a joke.

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