British officers in the city of Birmingham trial body-worn cameras (West Midlands Police/Flickr)

It may be the most significant reform to follow the fatal police shooting of Michael Brown.

On Monday, President Obama requested $75 million in federal funds for a technology that, as he sees it, could help bridge the kinds of rifts between the police and public that surfaced in Ferguson, Missouri. It's a technology that Brown's own family has championed as a "positive change" that could result from the teen's death. The White House has proposed distributing some 50,000 body cameras to police departments across the country, since "evidence shows that body worn cameras help strengthen accountability and transparency, and that officers and civilians both act in a more positive manner when they're aware that a camera is present."

But does the evidence actually show this? A grand jury's decision on Wednesday to not indict an NYPD officer for placing Eric Garner in a deadly chokehold in Staten Island brought out the skeptics. The chilling confrontation wasn't caught on a body-worn police camera, but it was filmed by a bystander:

Over and over again police shootings caught on camera and no indictment comes.Body cameras don't mean accountability. http://t.co/tgWtF8TFFi

— Nikole Hannah-Jones (@nhannahjones) December 3, 2014

Eric Garner's death WAS captured on video. We all saw it. Body cameras for cops won't solve this problem. It's bigger than technology.

— ∇ ▼Jenna Wortham ▼∇ (@jennydeluxe) December 3, 2014

Barak Ariel, a criminologist at the University of Cambridge, isn't so sure about body cameras, either.

The technology is "surely promising, but we don't know that it's working," Ariel told me. The Food and Drug Administration doesn't approve drugs until they've been studied extensively, he explained, and governments should take a similar approach with body-worn cameras. It's a solution that has yet to be proven.

Ariel should know. He's currently researching the effects of body cameras on policing everywhere from Brazil to Ghana to Israel to Northern Ireland, and finding that some police departments (and police unions) love the idea and others hate it. Nearly all of these tests have yet to be completed, but Ariel recently co-authored a study on the practice in Rialto, California, where he found that police officers who weren't wearing cameras were twice as likely to use force as those who were. During the 12-month experiment, the police department also saw a reduction in citizens' complaints compared with previous years. The researchers concluded that the benefits of wearing cameras trumped the costs.

But Ariel insists that there isn't enough evidence so far to generalize the finding and assert that body-worn cameras offer a net benefit to community policing. The Rialto report, for example, was the world's first randomized-controlled trial involving the technology.

Consider the costs, both calculable and incalculable. There's the hefty price tag for the cameras (around $800 to $1,000 each) and the systems to store and sift through the data they collect. Equipping frontline police officers across the U.S. with cameras, and paying the monthly subscription fees for their use and upkeep, could cost billions of dollars, Ariel estimated.

There are also privacy concerns—the fear, as one editorial in Canada's Globe and Mail recently expressed it, that cameras "could turn every officer into a mobile, closed-circuit camera, hooked up to a database tracking and recording people’s movements across the city." People could refrain from reporting incidents to the police because they don't want to appear on camera. Ariel is less worried about increased surveillance—"I don't think there's a single street in London that isn't covered by CCTV [closed-circuit television]," he points out—than about what data is stored and how that evidence is used. Those are questions that each country's legal system will have to sort out.