A grand jury has decided not to indict two Cleveland police officers over the fatal shooting of 12-year-old Tamir Rice.
Tamir was carrying a pellet gun when rookie patrolman Timothy Loehmann opened fire on the black youngster in November 2014.
Footage of the fatal shooting recorded by a surveillance camera fuelled a national protest movement over police killings.
A grand jury began reviewing the case in October to determine whether Loehmann or his partner Frank Garmback should face criminal charges.
In announcing the panel’s decision on Monday, Cuyahoga County Prosecutor Tim McGinty said a “perfect storm of human error” led to Tamir’s death, but the officers’ actions did not amount to a crime.
In a statement, Tamir’s family said they were “saddened and disappointed … but not surprised” by the grand jury’s decision.
They accused Mr McGinty of “abusing and manipulating the grand jury process to orchestrate a vote against indictment”.
A federal civil rights lawsuit filed by the family against the two officers and the city of Cleveland is pending.
The officers encountered Tamir after responding to a 911 call about a man waving a gun at a Cleveland playground.
Within two seconds of their police cruiser skidding to a stop, Officer Loehmann exited the vehicle and opened fire.
On Monday, Mr McGinty told reporters that newly enhanced video showed it is “indisputable” that Tamir was removing his gun from his waistband when he was shot.
He said Tamir most likely intended to hand the airsoft pistol to the officers or to show them it was not a real weapon.
“But there was no way for the officers to know that because they saw events rapidly unfolding in front of them from a very different perspective,” Mr McGinty said.
“Believing he (Loehmann) was about to be shot was a mistaken, yet reasonable belief given the high stakes circumstances … he had reason to fear for his life.”
Assistant prosecutor Matthew Meyer said CCTV footage showed the boy repeatedly drawing the gun from his waistband and putting it back before the officers arrived.
He was also seen pointing the pistol at other children, Mr Meyer said.
Mr McGinty used the news conference to urge toy gun manufacturers to do more to make the airsoft pistols look like toys and not real weapons.