CLEVELAND, Ohio -- A Cuyahoga County grand jury on Monday elected not to bring criminal charges against the two Cleveland police officers involved in last year's fatal shooting of 12-year-old Tamir Rice.

The decision not to indict officers Timothy Loehmann and Frank Garmback brings to an end a months-long criminal investigation into the high-profile shooting.

Monday's decision comes more than 13 months after the shooting, which catapulted Cleveland into the national debate about police use of force.

Cuyahoga County Prosecutor Timothy J. McGinty, whose oversight of the grand jury process drew criticism, called the shooting "a perfect storm of human error" while announcing the grand jury's decision at a news conference.

The grand jury heard evidence over nearly three months, including conflicting reports written by five experts in police use of force, statements read by Loehmann and Garmback and testimony from some of Tamir's relatives who arrived within minutes at the scene of the shooting.

In their statements, the officers each wrote that they saw Tamir pulling what they thought was a real gun out of his waistband before Loehmann shot the boy from close range.

Loehmann and Garmback arrived at the Cudell Recreation Center about 3:30 p.m. on Nov. 22., 2014, after a man reported a "guy with a pistol" was scaring people. Tamir had been playing with a replica pellet gun with the orange safety tip removed. The caller also said that the gun was "probably fake" and that the suspect was "probably a juvenile," but those details were not relayed to the officers.

Garmback drove the police cruiser into the park toward the gazebo where Tamir had been sitting. The boy approached the car with his hands toward his waist. Loehmann jumped from the passenger side of the cruiser and fired twice.

The entire interaction, captured by a city-owned surveillance camera, lasted less than two seconds. Loehmann wrote that he shouted four times for Tamir to show his hands before he opened fire.

The Cuyahoga County Prosecutor's Office released three reports from national experts in police use of force that each found the boy's shooting was tragic but reasonable because the officers did not know Tamir's age or that the gun was fake. The experts also concluded that a reasonable officer responding to a report of a man with a gun would have considered Tamir's movements around his waist to pose a "threat" to their safety. They also concluded the use of deadly force would be legally appropriate.

The reports drew ire from lawyers representing Tamir's mother, Samaria Rice, in a wrongful death lawsuit against the officers and the city. The lawyers accused the experts of being too deferential to law enforcement. The attorneys eventually released reports from three of their own experts, two policing experts and a bio-kinetics expert, who concluded that the shooting was unreasonable and that Tamir's hands were actually in his jacket pockets when Loehmann fired.

The lawyers, community activists and a group of rabbis and pastors had called for months for McGinty to allow a special prosecutor to take over the investigation. They accused McGinty of harboring a bias in favor of law enforcement because his office works with police officers to build cases, and seeking expert reports that would exonerate the officers.

They also wrote a letter earlier this month asking the U.S. Department of Justice to intervene and conduct its own criminal investigation. The office of U.S. Attorney for the Northern District of Ohio Steven Dettelbach is reviewing the letter, though such an intervention would be extremely rare.

McGinty has argued that every prosecutor in the country works with police officers, and that his office has prosecuted several police officers in the past. He said recusing himself from the investigation without a direct conflict would violate his oath to investigate every case, including the difficult ones.

Cleveland Municipal Judge Ronald B. Adrine wrote a non-binding opinion in June saying that there was probable cause for Loehmann to face murder, involuntary manslaughter and reckless homicide charges. His opinion also said that Garmback could face a charge of negligent homicide.

Adrine offered the opinion in response to a group of community activists and attorneys who invoked a seldom-used law that allows citizens to seek charges.

The shooting marked the first time Cleveland asked an outside agency to probe a police use-of-force incident. The city announced Jan. 1 that police would hand the investigation over to the Cuyahoga County Sheriff's Department, which conducted a three-month investigation and gave its evidence to McGinty's office in June without making a recommendation.

The Cleveland police department also has come under tense scrutiny after a U.S. Department of Justice investigation found that officers were too quick to use force against suspects and that the system to investigate civilian complaints was "woefully inadequate."

The city agreed earlier this year to enact sweeping police reforms that will be monitored by a federal judge for a minimum of five years and likely cost millions of dollars.