Campbell police Officer Matt Ryan, who is wearing a camera, takes a call from headquarters while driving in the city. Photo: James Tensuan, The Chronicle

Police departments around the Bay Area and the country are equipping officers with wearable cameras in an effort to capture video evidence that could head off the kind of dispute that exploded after an officer killed an unarmed teenager in Ferguson, Mo.

Use of the cameras is now expected to swell, with Ferguson among the cities planning to buy them as part of a profound shift in law enforcement that comes two decades after the mass emergence of videos of violent police encounters.

But while police leaders and critics are in rare agreement over the cameras – the watchdogs see accountability, the police see a way to protect officers from unfounded accusations – the technology’s spread is raising questions.

In some cases, including a friendly-fire shooting that left a BART sergeant dead in January, officers failed to turn on cameras at crucial moments. Attorneys for people shot by police have had to sue to see footage. And it remains a point of debate whether an officer who shoots someone should be able to review the video before making an official statement.

Moreover, videos of police shootings do not necessarily calm debate over whether they are justified. Police in St. Louis released a cell phone video this week of two officers killing a suspect who advanced with a knife, an effort to show the shooting was warranted in the wake of the controversial killing of 18-year-old Michael Brown in nearby Ferguson, which was not video-recorded.

Cops, critics disagree

But some who watched the St. Louis video online felt the officers used excessive force. Police officers and their critics differ on what constitutes a justified shooting.

“These cameras are viewed as the ultimate silver bullet, but they’re not,” said Barry Donelan, president of the Oakland Police Officers’ Association. “They’re another great tool in policing, but they have limitations just like everything else.”

The Oakland Police Department, which is under court order to tighten control over its officers’ conduct, has about 800 chest-mounted cameras made by VIEVU, a Seattle company that urges cops to “prove the truth.”

Other Bay Area police forces that have outfitted officers with cameras made by VIEVU or Arizona-based Taser International include Union City, Los Gatos, Gilroy, Brentwood, Vallejo and Campbell. The Taser cameras work like digital video recorders – when activated they preserve footage from the previous 30 seconds along with anything that happens in the future.

Early evidence suggests the cameras may have a powerful effect on both police and people they encounter: Police officials in Rialto (San Bernardino County) said their deployment of Taser cameras in February 2012 reduced use-of-force incidents by 59 percent over the first year among officers who wore them. Citizen complaints fell 87.5 percent.

“They’ve proven to be very successful for us in not only capturing evidence of crimes, but in protecting our officers,” said Campbell police Capt. Gary Berg. “There have been times when citizens have come forward to complain about certain incidents, and when we go back to review those videos, it tells a very different story about how it happens.”

But police critics are watching the emergence of the cameras closely. They say police agencies need to develop firm policies to make sure the public benefits from them.

Lack written policies

Steve Lovell, the president of VIEVU and a former Oakland sergeant, said that while 12 percent of police departments in the country now use body-worn cameras, nearly one-third do so without written policies.

“If you simply give the officer the ability to turn the camera on and off, what’s going to happen is that the officer will select what he or she thinks is important,” said San Francisco Public Defender Jeff Adachi. “That’s not going to give a complete picture.”

Adachi thinks the cameras should run constantly – though that may not be possible with the battery life and data storage on current models. Adachi has been a supporter of body-worn cameras since surveillance video showed San Francisco police officers purportedly entering rooms in residential hotels without warrants.

He released the footage to the public, which resulted in a federal indictment of six officers earlier this year and a grant-funded pilot program equipping about 50 plainclothes San Francisco officers with body-worn cameras.

Though the cameras in San Francisco are used mostly for searches, Adachi said he hopes they will spread to patrol. He said that if the police killing of Alex Nieto – who was shot in March in Bernal Heights Park while carrying a stun gun – had been caught on video, there would be fewer questions surrounding his death.

“There are different versions of what happened out there, and that’s always true in any case I’ve seen,” Adachi said. “But when you have video, that is objective evidence. Physical evidence does not lie and video does not lie. It doesn’t always solve the case, but it gives you a visual image of what happened.”

Advocates for police officers support the use of body-worn cameras for the same reason, but some caution that the footage is just one piece of evidence.

In the Bay Area’s first police shooting to be captured on a body-worn camera, an Oakland officer killed 34-year-old Arthur Raleigh on Cherry Street during a foot chase in September 2011. The video showed Raleigh had a gun before he was shot by Officer Bryan Franks, but it did not show Raleigh pointing it at the officer’s chest – which is what the officer said happened, said Terry Leoni, the officer’s attorney.

Not the whole picture

Former Police Chief Howard Jordan initially sought to fire Franks, but changed his mind after reviewing more evidence. Leoni said he was reprimanded.

“These videos don’t show the whole picture,” Leoni said. “They don’t show fully what the officer sees. His chest might be facing to the right, which is what happened on Cherry Street, but his eyes and his face are looking at something else, which is a gun pointed at his arm and his chest.”

Unlike a cell phone video that goes viral, the Cherry Street video has never been released publicly. John Burris, the attorney for Raleigh’s family, said he had to sue Oakland to get it. He said that’s often the case in use-of-force investigations.

“The police are reluctant to give up any items, including the name of the officers,” Burris said. “It’s very frustrating for the families. They’re already suffering because of what happened, and even if their family member is in the wrong, they have the right to know and they should know sooner rather than later.”

In at least two other Bay Area police shootings, officers apparently failed to turn on their cameras.

Camera not running

In Oakland, Officer Miguel Masso did not have his camera running when he shot and killed 18-year-old Alan Blueford in May 2012 after chasing him through a darkened neighborhood. Masso said Blueford had a gun and that he fired in self-defense when Blueford made a threatening move – an account disputed by the teenager’s family.

In January, the tragic accidental shooting of BART police Sgt. Tom Smith by a colleague, during an apartment search in Dublin, was also not caught on video. Sources told The Chronicle that the five officers who entered the apartment either weren’t wearing the devices or didn’t activate them.