In making the case to tie Mayor Brandon Johnson’s hands on canceling the ShotSpotter contract, City Council members have repeatedly cited faster response times and the number of gunshot detection alerts not accompanied by a 911 call.

South and West side alderpersons representing the city’s most violent police districts have argued that Chicago police officers never would have known about those incidents without ShotSpotter.

Now, they have statistics to back up their anecdotal claims.

The statistics, compiled by the Chicago Police Department, show response times over the past six years were more than two minutes quicker with a ShotSpotter alert than when the gunshot detection alert was accompanied by a 911 call.

With only a ShotSpotter alert, the average response time was 8 minutes, 6 seconds. That compares with 10 minutes, 11 seconds when ShotSpotter was combined with a 911 call. Response time grew to 10 minutes, 48 seconds with a 911 call but no ShotSpotter alert.

Those six years of numbers also show officers got a ShotSpotter alert alone nearly three times as often as when the gunshot detection alert was combined with a 911 call.

The disparity was particularly wide in the city’s most violent districts.

For example, the Englewood police district had 17,775 ShotSpotter-alone alerts versus 5,719 combined 911/ShotSpotter notifications from Jan. 1, 2018, to March 31, 2024. The difference in the Calumet District on the Far South Side was 23,316 versus 8,865 and in Harrison on the West Side, 15,030 versus 6,040.

When there was both a 911 call and ShotSpotter alert, officers were more likely to render aid to a victim than with a gunshot alert alone.

Numerous studies have shown ShotSpotter hasn’t lived up to all its promises. It was pitched as reducing shootings in high-crime areas, but a study released in January by Northeastern University in Boston found the alerts didn’t reduce fatal shootings or other gun crimes and didn’t lead to solving more shooting cases.

But the study, funded by the U.S. Justice Department, also said ShotSpotter sped up the response of emergency services to shootings, got cops to shooting scenes more quickly and led to seizing more guns.

The new Chicago statistics were provided in response to questions posed on April 1 by crime-weary Council members prepared to declare their independence from Johnson — at least in terms of keeping the controversial gunshot detection technology.

At that same meeting, the Committee on Police and Fire approved an order, championed by South Side Ald. David Moore (17th), that would allow each local alderperson to decide whether to keep ShotSpotter in their ward.

It also would prohibit the mayor from eliminating the technology in a ward where the local alderperson supports it without first getting full Council approval. Members keeping ShotSpotter would be protected from mayoral retaliation.

The order further mandates CPD to collect more specific data to justify signing a new long-term contract with ShotSpotter instead of terminating the agreement on Nov. 22, as called for under the nine-month extension that Johnson hastily negotiated at a rate significantly higher than the city paid for the entire past year of service.

The information that now must be collected and publicly reported includes incidents when ShotSpotter sensors detect gunshots but nobody calls 911 to report a shooting. CPD must also report the rates at which shell casings and weapons are recovered after ShotSpotter alerts, the rates at which alerts lead to arrests, and the varying response times to alerts and 911 calls without the gunshot detection technology.

That’s the kind of information that has now been provided to alderpersons as they prepare to take a final vote on Moore’s order at the May 22 City Council meeting. Some of the mayor’s staunchest Council supporters are among those pushing to keep ShotSpotter amid a furious behind-the-scenes lobbying campaign that had the company, now known as SoundThinking, helping to draft the order.

Johnson canceled the ShotSpotter contract, keeping a campaign promise and delighting his progressive supporters. But well aware the technology has been embedded for years in the nerve centers of South and West side police districts, the mayor negotiated to extend ShotSpotter through the traditionally violent summer months. This year, that period includes the Democratic National Convention in August.

Johnson has argued the order stripping him of the power to cancel the ShotSpotter contract has no “legal standing.”

“There’s no process by which you could govern through a la carte,” Johnson told a news conference after last month’s Council meeting, adding there’s no way “to do that type of ward-by-ward contracting.”

The mayor said then he extended the contract to give Council members “time to think through other technologies” but won’t change his mind about canceling it.

“People who voted for me knew what my position was,” he said. “This didn’t just pop up.”

That sets the stage for a legal battle between the executive and legislative branches not seen since the power struggle known as Council Wars in the 1980s.