CLEVELAND -- Prosecutors in Ohio on Saturday released a frame-by-frame analysis of the surveillance camera footage first made public a year ago that shows a white Cleveland police officer fatally shooting a black 12-year-old boy who had a pellet gun.

The enhancement by a video expert will be presented to a grand jury that will decide if then-rookie patrolman Timothy Loehmann or his field training officer should be charged criminally for the death of Tamir Rice. Loehmann shot Tamir outside a Cleveland recreation centre on Nov. 22, 2014.

The analysis doesn't appear to contain any new or substantive information and doesn't clearly show whether Tamir, as police officials have maintained, was reaching into his waistband for the pellet gun when Loehmann shot him less than two seconds after getting out of the car.

In a statement, Cuyahoga County Prosecutor Tim McGinty said the new footage was released in the "spirit of openness."

The still images were taken by a security camera at Cudell Recreation Center. They show different angles than video of the incident previously released.

"Once again ... we are not reaching any conclusions from these or other isolated bits of evidence," McGinty said in a release. "Individually they are simply pieces of a complex puzzle."