Jury Duty, Part 6: 'Shotspotter'

In which a witness is grilled on his software and a bug in it

Today we heard from an expert analyst at the company called Shotspotter. This company places microphones around a city above the roof lines of the houses, microphones which are always listening for what they call an ‘impulsive sound’ which is basically a gunshot sort of sound. Should the system hear an impulsive sound, it will record it (including the 4 seconds prior to the start of the event and 4 seconds after the event ends), use multiple sources around the event to triangulate the position of the shots, and notify the police automatically.

A simplification of how it works was given to us: the recording is processed and checked for around 40 factors which can determine if it was a gunshot or something like a car backfiring. It can pick out individual gunshots from an automatic fire burst, like say of an Uzi type weapon, and record when each happened down to the thousandth of a second.

Shotspotter caught the impulsive sounds for this crime… sort of. It recorded the first 6 shots of the gunfire exchanged and then truncated everything after those first 6 shots. To reiterate: the software which is supposed to record 4 seconds, a series of gunshots, and 4 seconds, randomly stopped recording after about 6 seconds. The witness had no explanation for that, other than a potential software bug.

This whole witness was a strange thing. The area that our crime occurred in is OUTSIDE of the Shotspotter area of coverage by about 2 blocks. Because of that, the initial alert was filed for a location a few blocks away. After investigating, the witness re-triangulated the location to about 20 feet away from where the bodies were located on the crime scene diagram.

So not only is there a system that listens to the city at all times (though it in THEORY only records impulsive sounds), it isn’t very reliable when it comes to doing the thing that it is supposed to do: record events.

The funny thing about this witness is that I might have caused him to be summoned by pointing something out in a police report*. A witness previous to him was the 911 supervisor, and as we were going over the 911 report for the crime (report number 139) the lawyers attempted to muddle their way through reading it. It looks like the sort of thing you’d expect a police system to spit out: a bunch of lines of info that looks more like SQL than English.

Anyway, the defense saw mention of a report number 136 and just straight up latched on to that as evidence of… something? I’m not sure what their point was, to be honest, but they kept questioning her on it even though she said that she didn’t have the record in front of her and couldn’t tell them details.

While they kept on asking questions I read through the report, and 3 pages in there was a line about an association being made between 136 and 139, the latter being a duplicate of the former, the former being generated automatically by Shotspotter.

I wrote a note to the judge stating this. Unfortunately, my handwriting is that of a retarded child and he couldn’t read what I wrote. He asked the jury for clarification and I had to tell him the 9 was a 4, thereby outing myself as the one who wrote the note.

Seems like the DA did some digging into it, found the Shotspotter report and called the SS witness.

The witness from Shotspotter took up literally the entire day. It was exhausting.

*Our jury was allowed to write down notes and have them sent up to the judge; if the judge deemed it relevant, he would meet with the lawyers in his chambers and they’d all decide what to do about the note. 5050 it would not be acted on, but sometimes it’d be relevant and further information would be discussed.


The Jury Duty Saga