Tamir E. Rice, 12, is seen allegedly pointing a pellet gun at the Cudell Recreation Center in Cleveland, Ohio, in this still image from video released by the Cleveland Police Department November 26, 2014.[Photo/Agencies]

WASHINGTON -- A grand jury in Cleveland in the US state of Ohio on Monday acquitted a white police officer who shot and killed a 12-year-old black teenager last year.

The grand jury, which has been hearing the case since October, decided not to charge the officer, Timothy Loehmann, and his partner Frank Garmback.

It cited that it was difficult for the officers to tell the difference between a real gun and the pellet gun that the victim, Tamir Rice, was carrying at that time.

Rice was gunned down on Nov. 23, 2014 by Loehmann, 27, outside the Cudell Recreation Center. He and his training partner were responding to a 911 emergency call about a man pointing a gun at people in the center.

But it later turned out that Tamir was only playing with an air-soft gun that he borrowed from a friend. The gun looked like a real gun, but it can only fire nonlethal plastic pellets.

In explaining the grand jury's decision, Cuyahoga County prosecutor Tim McGinty said the officers had no way of knowing that the gun Rice was holding was not a real gun, so Loehmann was justified in opening fire at Rice for fear of his life.

McGinty attributed the shooting to "this perfect storm of human error, mistakes and miscommunications by all involved that day," adding that there was no evidence that indicates criminal conduct by police.

A video of the police shooting of Rice sparked rage nationally at police excessive use of force and discrimination against African Americans.

This incident, together with several other highlighted incidents involving police killings of black victims, helped create the black civil rights movement Black Lives Matter, which has been holding protests across the nation demanding justice for those black people killed by police.

Rice's family issued a statement Monday, condemning the grand jury's decision and accusing the prosecutor of "abusing and manipulating the grand jury process to orchestrate a vote against indictment."