UK gun crime: Should police retry gun sensor technology?
San Francisco is scaling up its use of an intelligent gunshot sensor system - but when the same scheme was trialled in the UK it was abandoned after two years. However, the technology of the sensors has improved, so is it time to retry the system?
It sounds like a no-brainer. A tried and tested network of listening sensors are placed around a city and can instantly pinpoint where a gunshot has come from within seconds of the weapon being fired.
ShotSpotter promises to save police having to hunt door-to-door in the vague vicinity of a blast. It analyses the way the sound waves from the gun firing radiate out reaching microphones at slightly different times.
Its maker SST says it can distinguish the sound of a bullet being fired from fireworks and other types of explosion, count how many shots were fired and even deduce how many gunmen were involved.
San Francisco is scaling up its use of the tech - and it's also been deployed in Miami, Boston, Puerto Rico and Rio de Janeiro.
But an effort to use it to combat gun crime in the UK was abandoned when authorities in the city of Birmingham reported "technical difficulties".
So, what went wrong - and would it be worth reconsidering?
In December 2010, West Midlands Police were optimistic about what the innovation could achieve.
The cost of investigating a single murder could run to £1m. By contrast, installing the system cost £150,000 and a further £21,000 a year to maintain.
"We're delighted to be the first city in the UK to secure this technology," said Ch Supt Chris McKeogh at the time.
Some residents expressed concern that their conversations might be picked up - a previous effort to install hidden CCTV cameras in the city had proven controversial and had to be abandoned - but the police assured them this would not happen.
But just 20 months later ShotSpotter was judged to be a second failure.
In August 2012 West Midlands Police said of 1,618 alerts produced by the system since November 2011, only two were confirmed gunfire incidents.
What's more, the force added, ShotSpotter had also missed four confirmed shootings.
Its conclusion was that resources would be best spent elsewhere.
Ch Supt Clive Burgess said the system had "struggled to work" and that in future officers would instead focus on day-to-day community policing, anti-gun education programmes and the work of the counter-gang task force.
Air gun problem
Now that the dust has settled, SST is willing to discuss what went wrong.
James Beldock, the firm's senior vice president of products, said the figures quoted two years ago were misleading.
"There were only two cases of an actual firearm shooting being missed [by SST] over an 18-month period," he said.
"The other two were air guns, which ShotSpotter is explicitly not designed to detect."
He acknowledged there were "technical problems", which caused the system to be less accurate than normal, but suggested this could have been avoided if the city had been more committed to the idea.
"SST originally proposed a density of ShotSpotter sensors of approximately 10 per square kilometre," he said.
"Such sensor densities are standard for our international deployments - Brazil, South Africa, Panama, etc.
"Unfortunately, budget constraints pushed West Midlands Police to reduce that density. We take partial responsibility for permitting the budget to drive the decision, along with West Midlands Police."
The firm had learnt from this mistake and made other changes to improve the system.
SST staff now monitor all the sensors deployed worldwide through a central base in the US to confirm the cause of each explosion, rather than leaving such a judgement to local law enforcers on the ground.
And a new generation of sensor - with approximately 10 times the processing power - has now been introduced, Mr Bedlock said.
Even so, Birmingham - and other UK cities that eyed ShotSpotter - might be wise to remain reticent.
ShotSpotter is optimised to handle the very specific noises, frequencies and decibel levels created by conventional weapons.
But while such weapons may be relatively easy to come by in the US and parts of Latin America, they are less common in the UK.
As a result, criminals in Britain often resort to other types of firearms, including ones that shoot pellets and electric stun guns.
A review of the 22 injuries caused by guns in Birmingham's west and central areas between April 2011 and March 2012 reveals that the majority were the result of air-rifles and BB air guns.
"A higher sensor density might permit such modified weapons to be detected, but the economic equation would, again, need to be reviewed," said Mr Bedlock.
It's not impossible that ShotSpotter will return to the UK. The Home Office notes that it is "down to each regional police force" as to whether it invests in the equipment.
But for now it seems this is one instance where the traditional trumps cutting edge tech - at least where British cities are involved.