As the one-year anniversary of the death of George Floyd approaches, one thing is certain: the protests and court proceedings after his murder in Minneapolis might never have happened without a bystander's video. Videos of many incidents across this country, are transforming law enforcement — from police training to prosecutions. It's a change that's been three decades in the making.

The searing video of four LAPD police officers beating Rodney King, 30 years ago, shocked the nation. It precipated a trial and five days of riots after the officers were acquitted. In 2009, a plethora of videos documented the shooting of Oscar Grant by a transit cop in Oakland, Calif. Five years ago, Philando Castile's girlfriend livestreamed his death online after he was shot by a suburban Minneapolis police officer during a traffic stop.

During Derek Chauvin's trial, this year, the prosecuting attorney told jurors, "believe what you saw" and they did — finding Chauvin guilty of murder and manslaughter. It was an example of a change in how people view incidents that involve police use of force. It showed an evolution of a police agency. Several Minneapolis officers including the chief of police, guided by video clips and police policy, testified against Chauvin.

Although there's been graphic video of police encounters, not all video makes it into a courtroom. The legal standards regarding rules of evidence about a video's credibility and authenticity are high. Even so, University of Washington Law School Professor Mary Fan, who studies how audio-visual technology is reshaping policing, says there's been a dramatic turn in how much video is used in court cases.

"Video evidence is volatile and emotional and it gives people a sense that they are seeing an objective window into what really happened and now they can figure it out," Fan says.

In the Chauvin trial, video was the star. On the witness stand, experts dissected videos. They gave detailed testimony about seconds in the bystander video that showed the former Minneapolis police officer with his knee on George Floyd's neck for more than nine minutes. Another video from a police body-worn camera showed the intense struggle that broke out when officers tried to get a handcuffed Floyd in the back seat of a squad car.

With the use of video on the rise in court cases, attorneys are also more sophisticated about tapping into its power. The prosecution and defense offered divergent interpretations of the harrowing scenes of George Floyd's arrest but getting a jury to see a video in the same light is key. Minnesota Attorney Gen. Keith Ellison, who organized the prosecution team, says they put a lot of thought into how best to use the videos.

"We wanted to emphasize the testimony of eyewitnesses and to help the jury understand the case as opposed to dumping video on top of them," Ellison said. So they asked questions like "Can you overplay the video? Can you overdo the video so you make people numb to it?"

Sharon Fairley, a law professor at the University of Chicago, says videos can be very strong trial evidence. A former federal prosecutor, Fairley also headed the agency responsible for investigating alleged Chicago police misconduct after a judge ordered the video release of a controversial police shooting. It showed the 2014 shooting of 17- year-old Laquan McDonald by Chicago police officer Jason Van Dyke. Van Dyke was convicted of second degree murder. Fairley warns that video doesn't guarantee a guilty verdict during a trial, but adds there are other ways it can be useful.

"We've seen a lot of these videos come out in the last few weeks and they are really hard to watch," she says. "They are heart wrenching but it's important because it's how we learn how the police department is operating so we can make change if appropriate."

Fairley calls it a reckoning for how we look at policing and for how police officers learn to do their job.

Police departments often use videos in training workshops. They review specific encounters in an effort to get officers to think ahead about what steps they could take to prevent them. Chuck Wexler is executive director of the Police Executive Research Forum, an organization of law enforcement officials and others that works to professionalize policing. He says he believes the bystander video and police body-worn camera video in the Chauvin trial will change how police departments train officers in the future.

"It used to be that police would say we don't want to Monday Morning quarterback," Wexler says. "Videos are making us think how we are training officers — what should have been done and how to intervene. So if you have an officer who's had a series of complaints, you can review their body-worn camera to see have they changed their behavior."

There has been some change. The state of New York banned the use of chokeholds in the aftermath of the deaths of George Floyd and of Eric Garner who was killed earlier, in 2014, after an NYPD officer put him in a chokehold. Both men repeatedly cried out that they couldn't breathe when restrained by police. In Chicago and elsewhere, policies now say an officer has a duty to intervene if they witness another officer using an excessive use of force or abusing a suspect. The body camera video is to be the witness.

While thousands of police officers wear body cameras, plenty don't. There are about 18,000 law enforcement agencies in the country and the Justice Department says only about half have the technology. Law enforcement agencies without cameras often cite the costs of the technology and the money needed to store and maintain hundreds of hours of data as an obstacle, according to Arizona State University Professor Michael White, co-director of training for the Department of Justice's Body-Worn Camera Program.

"But I think the train has left the station," White says. "Several things are incentivizing the adoption of this policy, one of which is public demand. The public expects police officers to wear body worn cameras and if an incident occurs and there's no footage the community is upset."

A new grant program will help smaller police departments pay for the cameras, White says.

However, there's still a lot of uncertainty over whether the technology is actually helpful. One of the main goals of using body-worn cameras is to see a reduction in police misconduct and police use of force. Results are mixed. During Chauvin's trial, for instance, a police officer in a Minneapolis suburb who was wearing a body camera, shot and killed 20-year-old Duante Wright during a traffic stop. The officer says she meant to use her Taser and not her handgun. She's been charged with second degree manslaughter.

Although tragic incidents continue, one of the latest studies about body-worn camera use shows the technology can be beneficial and cost effective. Research conducted by the Council on Criminal Justice and the University of Chicago Crime Lab found that in police departments where officers wore body-cameras, complaints against police fell by 17% and use of force by nearly 10%. Not a panacea say the researchers but a step. The other benefit? While video can validate claims of police abuse that have often been dismissed, it can also protect officers who may be wrongfully accused.

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