"We have cases like that all over the country where it can be a wallet, a cell phone, a can of Coca-Cola and officers have fired the weapon," said Scott Greenwood, a Cincinnati attorney who has worked on police use-of-force cases across the country and who is a general counsel for the American Civil Liberties Union.

"It does not necessarily mean it was excessive use of force," he added. "However, those types of incidents do give rise to greater suspicion on the part of the public about how police use force and they call into question the training departments are using to train officers to perceive and respond to threats."

The New York Police Department says the officers who fired 20 shots at 18-year-old Khiel Coppin on November 12 were justified in their use of force. The mentally ill teenager approached officers outside his mother's home with a black object in his hand, the hairbrush, and repeatedly ignored orders to stop.

The officers were responding to an emergency call in which Coppin could be heard in the background saying he had a gun. But in a second emergency call Coppin's mother told the operator her son was not armed, and after officers arrived she repeated that to them.