The District of Columbia, parts of which have been plagued by poverty and crime, has experienced so much gunfire that it averaged at least one gunshot every two hours over the past eight years.

This fact was derived from an analysis of data culled by The Washington Post after reviewing police records of a gunfire surveillance network known as ShotSpotter. Consisting of rooftop sensors mounted on buildings and light poles through the city, ShotSpotter notes every time the sound of firearms being discharged is detected.

Those sounds are analyzed by a computer and tracked to within yards of their source location—a process that takes less than 40 seconds per incident. Personnel monitoring the system notify police in the field, who then speed to the location. Once on site, law enforcement may find a shooting victim, evidence such as shell casings or, if they’re lucky, the shooter.

About 39,000 gunshots were documented by ShotSpotter over a period of eight years.

Records also showed that more than half of the incidents detected by the network involved multiple rounds of gunfire.

In 2009 alone, ShotSpotter captured more than 9,000 incidents of gunfire.

Since then, the annual totals have fallen by 40%, coinciding with a decline in gun-related murders in DC.

The system—manufactured by SST of Newark, California—provides a close approximation of gunfire incidents, but isn’t completely accurate. The DC network covers only a third of the city, targeting districts with the most violent crime. Some gunfire shots are missed if a silencer is used, a close-range execution-style murder takes place, or simply due to the acoustic nuances of the city landscape. Occasionally similar sounds, such as fireworks or car backfires, are mistaken for gun shots, but officials say these errors are usually caught and filtered out.

ShotSpotter was first installed in DC in 2005 with assistance from the FBI and a $2 million federal grant to set up sensors in a pilot district, selected because it led the city in homicides. An additional $3.5 million has been spent by the city in the past six years to maintain and expand the system.

The District of Columbia is now one of more than 70 metropolitan areas that have invested in ShotSpotter. It is also being used by police in Rio de Janeiro, and undergoing testing in a South African safari park to identify illegal rhinoceros poaching.

- Danny Biederman, Noel Brinkerhoff

To Learn More:

ShotSpotter Detection System Documents 39,000 Shooting Incidents in the District (by Andras Petho, David S. Fallis and Dan Keating; Washington Post)

South Florida Cops Hope ‘ShotSpotter’ Can Help Find Shooters (by Lance Dixon, Miami Herald)