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Acting under a rarely used provision of Ohio state law, a judge found probable cause Thursday to charge Cleveland police Officer Timothy Loehmann with murder in the fatal shooting of 12-year-old Tamir Rice last year.

Cleveland Municipal Court Judge Ronald Adrine also found cause to support negligent homicide charges against Officer Frank Garmback, Loehmann's partner, who is accused of standing by after Loehmann shot Tamir in November at a recreation center, where Tamir was playing with a pellet gun.

Adrine agreed with local activists known as the "Cleveland 8" who took the unusual step of independently seeking charges because, they said, they'd lost confidence in the grand jury investigation.

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The ruling is only advisory and doesn't affect the separate grand jury investigation.

Adrine — saying he wasn't performing an "end around" of the city or the county — said the choice to lodge charges remains with Cuyahoga County and Cleveland prosecutors. In a statement, county prosecutor Timothy McGinty said the grand jury would make any final decision.

The citizens motion, known as an "affidavit of person having knowledge of offense," centers on a widely distributed security video of the shooting.

In his 10-page ruling, Adrine called the video "hard to watch," saying he was "thunderstruck by how quickly this turned deadly." As Loehmann and Garmback look on and as at least six other officers arrive on the scene, it appears that Tamir is left to lie wounded on the ground for eight minutes with no indication that anyone is trying to help him, Adrine wrote.

Related: Read the Judge's Full Order (PDF)

Adrine found that there was enough evidence to justify charges of murder, negligent homicide, reckless homicide, involuntary manslaughter and dereliction of duty against Loehmann — but not aggravated murder, the most serious charge the activists had sought.

Garmback, he said, should face only negligent homicide and dereliction charges.

In a statement issued through their attorneys, Tamir's family praised "the efforts of the 'Cleveland 8' who exercised civility and intellect by invoking Ohio Citizen Participation laws Tuesday."

The ruling, they said, is "a blueprint for the nation to follow" in confronting "many of the relationship problems between African-Americans and law enforcement."

Loehmann's attorney, Henry Hilow, stressed that the ruling doesn't affect the county investigation, telling NBC News: "We respect the authority of the Cuyahoga prosecutor to review and investigate this case."