Officials are urging calm as they brace for expected protests after a grand jury voted not to indict a white Cleveland police officer for fatally shooting a 12-year-old black boy who was carrying what turned out to be a pellet gun.

Small groups of protesters gathered Monday outside the Cuyahoga County Justice Center and at the recreation center where Tamir Rice was shot by then-rookie patrolman Timothy Loehmann in November 2014. The size of those protests likely was reduced by a cold and steady rain that fell throughout the day.

County Prosecutor Tim McGinty announced that Loehmann and his field training officer wouldn't be indicted because of "indisputable" evidence that Tamir was reaching for what officers thought was a real gun tucked in his waistband, and urged those who disagreed with the grand jury to protest peacefully.

"It is time for the community and all of us to start to heal," McGinty said.

Cleveland Mayor Frank Jackson made a similar plea, as did Tamir's family. Attorneys for the family condemned the grand jury's decision but called on people to express themselves "peacefully and democratically." Deputies set up metal barricades outside the Justice Center after McGinty's news conference on Monday afternoon.

Outside the recreation center, protesters chanted, "No justice, no peace!"

Cleveland resident Art Blakey held a sign that read, "Indict, Convict, Send Killer Cops to Jail!" He said he wasn't surprised by the grand jury decision.

"There never has been any justice in these police murders," he said. "We're supposed to swallow these things whole as if this is business as usual."

Activists have said they're planning a protest outside the Justice Center on Tuesday afternoon.

The grand jury had been meeting several times a week since mid-October to hear evidence and testimony about the shooting. McGinty said he recommended to the grand jury that Loehmann and patrolman Frank Garmback not be indicted because they had no way of knowing that Tamir was carrying an Airsoft-type gun that shoots nonlethal plastic pellets instead of the actual firearm it's modeled after, a Colt semi-automatic pistol.

A man called 911 that November afternoon to report that a "guy" was pulling a gun out of his pants and was pointing it at people. He also told the dispatcher that it might be a juvenile and the gun might not be real. But the 911 call taker didn't relay that information to the dispatcher who gave the officers their high-priority radio assignment for what is known in police parlance as a "gun run."

"Simply put, given this perfect storm of human error, mistakes and miscommunications by all involved that day, the evidence did not indicate criminal conduct by police," McGinty said.

There was no immediate comment from Loehmann after the decision was announced. An attorney for Garmback issued a statement that said the officers "acted within the bounds of the law."

Steve Loomis, president of Cleveland's largest police union, said the organization was pleased with the grand jury's finding but added the decision "is no cause for celebration, and there will be none."

In a statement, Tamir's family said it was "saddened and disappointed by this outcome — but not surprised." It accused the prosecutor of "abusing and manipulating the grand jury process to orchestrate a vote against indictment."

A video of the shooting recorded by a surveillance camera and released publicly in the days following Tamir's death sparked outrage and helped fuel the national Black Lives Matter protest movement that gathered momentum after black men were killed by police in Ferguson, Missouri, and New York City. Officers in both of those killings were cleared of criminal charges by grand juries.

The surveillance video shows Loehmann shooting Tamir less than two seconds after he emerged from a police cruiser driven by Garmback that skidded to a stop just a few feet from the boy.

Loehmann and Garmback's legal issues haven't ended with the grand jury decision. Jackson said the city will begin an internal review to determine whether the officers should be disciplined for their roles in the killing. The officers and the city are being sued by Tamir's family in federal court, and a spokesman for the U.S. Attorney in Cleveland said Monday that there's an ongoing civil rights investigation concerning Tamir's death.

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Associated Press reporters Mitch Stacy, Kantele Franko and Julie Carr Smyth in Columbus, John Seewer in Cleveland and Dan Sewell in Cincinnati contributed to this report.