JUDY WOODRUFF: In the aftermath of the police shooting in Ferguson, Missouri, and the chokehold death of a man in New York City, civil rights groups and even the president have called for an increase in the use of body cameras by police departments.

Hari Sreenivasan takes us to one town where they recently began using them.

DANIELLE TORRES, Evesham Township Police Department: It's green. I'm ready to go out on a shift. I pick it up. I put it on. I flick it so that it's like that. Once it turns green, then it's ready for me to start recording.

HARI SREENIVASAN: For the last five months, police officer Danielle Torres has been wearing a small body camera when she's out policing the streets of Evesham, New Jersey, a commuter town just 20 miles southeast of Philadelphia.

DANIELLE TORRES: The body camera sees everything from me out, almost as if it's my eyes, whereas in-car cameras only see a stationary view of what's in front of my patrol car.

HARI SREENIVASAN: Her department is one of dozens across the country that have adopted this surveillance equipment.

And Chief Christopher Chew, who himself wears one, says his officers have all embraced the new policing tool.

CHRISTOPHER CHEW, Evesham Township Police Department: They see the benefits, not only short term, but long term, because it's there to protect them. It's there not only to protect against the frivolous lawsuits or complaints, but also it's capturing what they're doing, because they're doing great work each and every day.

And now they have the ability to capture it, go to court and show that they were doing the right thing. Our officers, they want everything recorded and audio to protect them.

HARI SREENIVASAN: The equipment is expensive. Cameras can cost up to $1,000 a piece, with data storage costs far exceeding that.

Earlier this month, President Obama asked that $75 million be spent to purchase such cameras for departments all across the country.

PRESIDENT BARACK OBAMA: I'm going to be proposing some new community policing initiatives that will significantly expand funding and training for local law enforcement, including up to 50,000 additional body-worn cameras for law enforcement agencies.

HARI SREENIVASAN: The move comes in the wake of the shooting death of Michael Brown by a police officer in Ferguson, Missouri, last August, an incident that wasn't captured on video.

DAVID HARRIS, Professor, University of Pittsburgh School of Law: As soon as that event happened, the immediate reaction was, where's the video? How come they don't have video?

HARI SREENIVASAN: David Harris is a professor at the University of Pittsburgh Law School. He predicts body cameras will soon be widely used by departments everywhere.

DAVID HARRIS: Police need to take this on, on their own terms, to have their own ways of looking at this. They have to put these on police officers. The public will be served because there can be greater accountability, there can be a much better, more nuanced record.

And the police, I think, have begun to realize, just like they did years ago with dash-cams, that their interests will be served as well.

HARI SREENIVASAN: Still, even Harris concedes that body cameras don't necessarily mean police will be held more accountable.

ERIC GARNER: I was minding by business, officer.

HARI SREENIVASAN: Earlier this month, a New York City grand jury decided not to indict an officer in the chokehold death of Eric Garner, in spite of the fact that the incident was videotaped by bystanders.

DAVID HARRIS: We know that, even if you see it on camera, there can still be biases. You don't have more than one camera angle, or the particular one you have only shows one part of the action, or you have situations in which there has been editing.

HARI SREENIVASAN: Jay Stanley, a policy analyst with the American Civil Liberties Union, agrees the jury is still out on the effectiveness of these cameras. His organization has given qualified support of their use if strict, consistent privacy policies are adopted.

JAY STANLEY, American Civil Liberties Union: There need to be very good policies to ensure that video footage that police take — and a large proportion of calls are domestic violence. Police are entering people's homes. They're seeing people at the worst moments of their lives — is not going to end up on YouTube or be passed around among police officers for laughs or what have you.

So there need to be very, very tight controls over the video data that is collected, who has access to it, how long it is retained, what it is used for.

HARI SREENIVASAN: And Stanley says officers cannot be allowed to alter the footage.

JAY STANLEY: The crucial thing is that police officers not be able to edit on the fly by turning the cameras off and on at will, or if they get involved in a dubious incident, finding a way to make sure that the footage disappear, all of which we have seen happen around the country.

HARI SREENIVASAN: Although body cam rules vary widely from city to city, the Evesham Police Department says it has taken precautions against those abuses. The cameras are recording all the time, although footage is only saved starting 30 seconds prior to an officer hitting the button. That footage is then automatically uploaded to the cloud at the end of every shift. And a digital record is kept of anyone who tries to access it.

DANIELLE TORRES: After a shift, you take the camera off, turn it off, and put it right in one of these ports as you see the other ones. And it will go through the process of downloading all the videos on the cloud.

HARI SREENIVASAN: So, that means you can't edit the video, you can't delete the video?

DANIELLE TORRES: Not at all.

HARI SREENIVASAN: Advocates of the cameras say widespread use could lead to better behavior by everyone involved. They point to several studies.

The Rialto, California, Police Department found there was a 59 percent reduction in the use of force by officers and an 88 percent reduction in complaints after body cameras were used.

And in a controlled study in Mesa, Arizona, where only half the force was given cameras, there were three times more complaints lodged against officers without cameras than officers who wore them.

So, how do you expect body cameras to change how an officer behaves?

CHRISTOPHER CHEW: Well, the officer now knows that everything they do when they have a contact with a citizen is now audio- and video-recorded. It puts them on another level. They now know that we have the ability as an organization to go back with checks and balances to ensure that they're following proper protocols.

HARI SREENIVASAN: Does it change the behavior of citizens once they know they're on camera by the police?

CHRISTOPHER CHEW: I would say, naturally, it would.

HARI SREENIVASAN: If authorized by Congress, the federal money for new body cameras would nearly double the number of cameras that are currently in use.