While an increasing number of police departments have the cameras, the rules governing their use can be unclear.
Two white Louisiana police officers will not face federal charges over the shooting of a black man whose death sparked widespread protests, the US justice department said, in a decision slammed by rights groups as a message of impunity.
The officers still face a state criminal investigation over last summer’s shooting of Alton Sterling, 37, in Baton Rouge, the state capital.
Wednesday’s decision not to bring federal charges was the first ruling in such a case under President Donald Trump’s attorney general, Jeff Sessions.
The case was being closely watched as both Trump and Sessions have criticised the Obama administration, saying it targeted police unfairly in civil rights investigations.
Sterling was shot dead July 5, 2016 in a scuffle with two officers, Blane Salamoni and Howie Lake, outside a convenience store where he had been selling CDs.
During a 10-month probe, FBI agents and prosecutors reviewed images of the incident captured by body cameras, mobile phones and store surveillance cameras as well as witness accounts and other evidence.
At the close of the investigation, the justice department said it found “insufficient evidence to support federal criminal charges” against either officer, in part because investigators could not determine whether Sterling was reaching for a gun at the time he was shot.
The shooting was one in a series of racially charged police killings that inflamed a national debate over treatment of minorities by law enforcement.
‘Give us justice’
Sterling’s family held a news conference on Wednesday to call on Louisiana Attorney General Jeff Landry to pursue state criminal charges.
“Open up your heart, your eyes, and give us the justice that we deserve,” said Quinyetta McMillon, the mother of Sterling’s oldest son.
Landry warned that a state investigation into the actions of the officers, which was delayed to allow the federal probe to proceed, “could take a considerable amount of time”.
In statements, the officers said that Sterling was attempting to pull a loaded gun out of his pocket when Salamoni opened fire, according to the justice department summary.
Videos of the incident did not conclusively show Sterling’s hand when the first shot was fired, making it impossible to prove the officers’ account was untrue, the department said.
Two witnesses who said his hand was not in his pocket gave accounts that were inconsistent in other details.
The two officers are on paid administrative leave pending an internal police investigation.
‘Black lives do not matter’
The head of the Southern Poverty Law Center called the decision not to press charges “deeply troubling”.
“The American people need an answer as to why the final moments of Sterling’s life looked less like a police stop and more like a public execution,” said its head, Richard Cohen.
Civil rights group Color of Change said the decision showed that, as far as Trump’s administration was concerned, “black lives do not matter”.
Wednesday’s events came a day after a white former South Carolina officer pleaded guilty in the 2015 shooting of an unarmed black man and a Texas officer was fired for shooting an unarmed 15-year-old boy on Saturday.
Attorney General Sessions is still responsible for deciding whether to bring charges in other high-profile police killings, including the 2014 chokehold death of Eric Garner in New York and the shooting of 12-year-old Tamir Rice in Cleveland that same year.