AUDIE CORNISH: As we just heard, Eric Garner suffered from asthma. It was severe. But again, while that played a role, the New York City medical examiner found Garner died from compression of his chest due to his restraint and the chokehold at the hands of police. Joel mentioned that the chokehold is banned under NYPD policy, but reports of zits use persist. Christopher Dunn of the New York City Civil Liberties Union tells us the debate over the chokehold goes back 20 years.

CHRISTOPHER DUNN: There was a highly publicized incident in 1994 where a police officer used a chokehold on a young man who was playing football. The football hit a police officer's car. Cops got out, applied a chokehold, and the man died. The department shortly thereafter instituted a complete ban on chokeholds which remains in place to this day.

CORNISH: But I understand over the years the definition of a chokehold has changed somewhat.

DUNN: Well, I think perhaps the understanding of it has. The policy is quite clear. It says - and I'm reading it - (reading) any pressure to the throat or windpipe which may prevent or hinder breathing or reduce intake of air.

That is the definition that's been in place for a long time. The problem has been that police officers and oversight bodies themselves have taken a looser and looser view of chokeholds leading up to the most recent incident involving Eric Garner.

CORNISH: Now, chokeholds are not illegal, but, as we've said, they are clearly barred by NYPD policy. But clearly people are still accusing the department of using the tactic. How widespread? Do we have any sense of that?

DUNN: Well, we don't have a great fix on how widespread it is. What we do know is that over the last five years, civilians have filed about a thousand complaints with the New York City agency that oversees these misconduct complaints. That's a much bigger number than anyone would have expected given the absolute ban on chokeholds. And there was a recent study from that agency that suggested that that number may actually have understated significantly the actual number of chokeholds being used by police officers.

CORNISH: How common is it for any of these claims to end in any kind of disciplinary action? Are these cases very difficult to prosecute?

DUNN: Well, it's very rare for them to result in disciplinary action. Our New York City Agency only substantiated 10 of those complaints over the course of the last five years, and even fewer of those officers were disciplined. And in our view that creates a culture where police officers feel like - and may be being told implicitly that they can get away with misconduct. And that's a very bad situation for us to be in.

CORNISH: Chris Dunn - he's the associate legal director of the New York Civil Liberties Union. Thanks so much for speaking with us.

DUNN: Thank you. Transcript provided by NPR, Copyright NPR.