GEOFF BENNETT: The use of police body cameras has become much more widespread in recent years, with the expectation that they will curb police violence and improve accountability.

As William Brangham explains, the promise of these cameras is falling well short of expectations.

WILLIAM BRANGHAM: Geoff, back in 2014, there were very differing accounts of what happened when 18-year-old Michael Brown was shot dead by a police officer in Ferguson, Missouri.

Was it justified self-defense or a fatal overreaction?

There was no body camera video to help answer that question.

Since then, departments across the nation have spent tens of millions of dollars to put small wearable cameras onto police officers.

And, in some shootings, they have made a difference, including murder charges in the deaths of George Floyd in Minneapolis, Tyre Nichols in Memphis, and, more recently, Eddie Irizarry in Philadelphia.

But a new investigation by ProPublica and "The New York Times Magazine" found it can often take months or years before video is released, if it is released at all.

Eric Umansky is editor at large at ProPublica, and he worked on this investigation.

Eric, great to have you back on the "NewsHour."

The promise, as I mentioned, of these cameras was to have this unbiased record of an event, and the belief being that, if police officers knew they would be seen in action, it might curtail bad behavior.

But your investigation showed how a lot of factors have undermined that promise.

What did you find?

ERIC UMANSKY, ProPublica: Sure.

So, primarily, what you have is the police who have been left in control of the footage.

And it's up to police to decide when footage is released, who it is released to, and what is released, whether it's the full footage or only partial footage.

And, as you mentioned, what we found is that often footage isn't released at all, and also, when the police themselves are in the sole custody of footage, they have often not acted on it to discipline, punish, or fire officers who do engage in problematic behavior.

WILLIAM BRANGHAM: And you cite many examples of where body camera video comes out much, much later after some tragic encounter, and it often directly contradicts what police said had happened in that moment.

Are there -- is there a particular example that stands out to you from your reporting?

ERIC UMANSKY: Well, so it's -- the example that I get into in the most depth in my story was actually the first police killing in New York ever captured on a body-worn camera.

And it's a young man named Miguel Richards.

It was a tragic and unfortunately all too kind of common incident where somebody was -- he was having a mental health crisis and was holding a knife.

Police came to his apartment and 15 minutes later he was shot 16 times.

The police commissioner at the time basically praised the officers, cited their exemplary restraint.

And the NYPD, while it released some footage, didn't release all of the footage.

And what all of the footage shows is that the officers' conduct was problematic, that help had been on the way with specialized training, specially trained officers.

And the officers at the scene just didn't wait and fired and killed him.

And yet those full facts six years later are only now coming out.

WILLIAM BRANGHAM: Your report also details how Derek Chauvin, the Minneapolis police officer who knelt on the neck of George Floyd, which eventually killed him, had done the same thing in many multiple examples prior to that, had been captured on body camera doing that, but that had never come to light.

I mean, is there any way to know how often demonstrable misconduct is captured on these cameras and then not brought to light?

ERIC UMANSKY: Well, that's actually part of the problem, is that it's really, really difficult to know.

Three years before Derek Chauvin killed George Floyd, supervisors had watched the footage.

They were the only ones who watched the footage, because the police had refused to release anything, and actually refused to release it even years after George Floyd's murder.

So it only came out after a judge ordered them to do so in a lawsuit.

WILLIAM BRANGHAM: What do police officials say when asked why they are reluctant or hesitant or simply don't release this type of video?

ERIC UMANSKY: Well, there are legitimate concerns about privacy in some cases, and that is one thing that they cite.

There are also particular laws.

So, in Minnesota, for example, the police in the city there cited a law that, when I looked into it, had been in its final form written by three legislators who had previously been police officers.

So legislators and the law plays a part in this as well.

WILLIAM BRANGHAM: It does seem like the refusal to release this video, the hesitancy to do so undercuts the entire idea that police officers know that they might be held to account, and thus might act more appropriately.

Viewers will remember the case earlier this year of Tyre Nichols, who was killed in Memphis.

This is actually what got me started on the story, is, there was a line in The New York Times about it which noted that officers had noted that their body-worn cameras were on and then proceeded to beat him anyway.

And you think to yourself, well, how could that happen?

The answer is that footage in Memphis is exceedingly rarely released.

The fact that footage was released in his case was an extraordinary exception.

WILLIAM BRANGHAM: All right, Eric Umansky, editor in chief at ProPublica, your reporting can be found in "The New York Times Magazine" and ProPublica.org.

Thank you so much for being here.

ERIC UMANSKY: Thanks for having me.