An Ohio grand jury has declined to indict the Cleveland police officer who fatally shot Tamir Rice, an unarmed black 12-year-old, in 2014.

Cuyahoga County Prosecutor Timothy J. McGinty announced the decision Monday afternoon, 401 days after rookie patrolman Timothy Loehmann shot Rice at a park in Cleveland. The grand jury also declined to indict veteran officer Frank Garmback, who responded to the scene with Loehmann, on charges of negligent homicide and dereliction of duty.

Tamirs family criticized the grand jury decision and in a statement accused McGinty of "abusing and manipulating the grand jury process to orchestrate a vote against indictment.

(Read the prosecutor's full report.)

On Nov. 22, 2014, Loehmann and Garmback were dispatched to investigate 911 calls about a "guy with a gun" pulling a weapon from his waistband and pointing it at people. The gun was later determined to be an airsoft pellet gun.

McGinty on Monday called Tamir's death a "perfect storm of human error," not a criminal act.

"The outcome will not cheer anyone, McGinty said, arguing that Loehmann's assessment that he was about to be shot was "a mistaken but sincere belief given the stress of the situation.

It would be irresponsible and unreasonable if law required a police officer to wait and see if the gun was real, McGinty said.

Officers said they believed Tamir to be a man in his 20s and that the orange safety tip on his toy gun was missing. An expert hired by McGinty's office conceded in a November report that dispatchers should have relayed to responding officers the 911 caller's observations that "the guy with a gun" was "probably a juvenile" and that the gun was "probably fake."

In statements filed with the Cuyahoga County Sheriffs Office, both officers claimed they repeatedly yelled at Tamir to "show me your hands." But surveillance video shows that Loehmann opened fire within two seconds of emerging from the police cruiser.