Acoustic experts detail purported Ferguson shooting

The purported audio recording of the shooting death of Michael Brown in Ferguson, Mo., reflects 10 shots all taken from the same place, according to acoustic experts who specialize in helping police identify urban gunshots.

The creators of ShotSpotter technology, used in 65 American cities, reviewed an audio recording aired by CNN that is claimed to have the Brown shooting in the background of an online videochat conversation. CNN said the man who discovered the gunshots in the background of a recording is working with St. Louis attorney Lopa Blumenthal.

ShotSpotter uses audio receivers in cities to identify and pinpoint shootings to speed police response and assist in investigations. There have been ShotSpotter antennas in St. Louis since 2008, but they are too far from the shooting that took place in Ferguson and did not pick up the incident.

When the purported recording was revealed earlier this week, the experts analyzed it, said Ralph Clark, chief executive officer of SST.

Ferguson Shooting Soundwave
ShotSpotter acoustic experts determined that the purported recording of the Michael Brown shooting has 10 gunshots marked in red, and seven echoes, marked in yellow. There is a three-second pause after shot six. The total time from shot one to shot 10 is 6.572 seconds. Experts said the shooter did not move, and the company could confirm the validity of the recording location if it is revealed.

While the company cannot verify the authenticity of the recording, Clark said it would be able to do if it were given the precise location of the shooting and the recording. His company can calculate the movement of the sound waves and confirm whether the recording was made in that location relative to the shooting, he said. At this time, the location of the recording has not been revealed, nor the precise location of the shooting that took place Aug. 9. The messaging software that captured the gunshot sounds in the background has verified that the recording was made at the time of the shooting.

Clark said the company confirmed that the sound on the recording is gunshots. His company specializes in distinguishing gunshot sounds from other noises like fireworks and car backfires. In addition, Clark said they could determine that the recording has 10 shots and then seven sounds that are echoes.

Clark said the recording has a three-second pause after the first six shots before the final four shots. His experts were also able to confirm that the shots were all taken from within a three-foot radius – there was only one shooter and that person was not moving.

“When you see the wave form file, other branches are effectively echoes,” he said. “It is mathematically consistent, the locations of primary muzzle blast did not move around for shots one through 10.”

Clark said he cannot say whether his company’s finding confirms or conflicts with the claims that a shot was fired inside the police patrol car, then subsequent shots were done outside the car.

Usually the company’s software uses multiple antennas to pinpoint the location of a shooting. In this case, he said, there is only one sound receiver, but the sounds bouncing off buildings can be used to make the same calculations that would normally come from multiple receivers. In effect, he said, the other buildings act like secondary recording locations because they can calculate the time it takes sound to travel between the buildings.

Dan Keating analyzes data for projects, stories, graphics and interactives. He was part of a team that won a Pulitzer at The Miami Herald for exposing vote fraud, and a team that was a Pulitzer finalist the year before for uncovering police fraud.
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