A grand jury will decide whether to charge the officer in connection with the death.
Rice was shot in a park while playing with a toy pellet gun. The officer who shot him, Timothy Loehmann, was responding to a 911 call about someone playing with a gun. The caller had told the operator the gun was probably fake.
The autopsy report found Rice was shot in the abdomen, with the bullet damaging an important vein and his intestines.
The shooting of Rice is only the latest case to raise questions about race and police officers' use of force following the deaths of two black men, Michael Brown in Ferguson, Mo., and Eric Garner in New York, at the hands of white officers. In both of those cases, grand juries declined to indict the officers, galvanizing protests across the country.
There are questions about whether Loehmann gave Rice any time to respond before he shot him. A video released by police shows that Loehmann fired on the 12-year-old boy two seconds after getting out of his patrol car.
Loehmann’s supervisor at a previous police job said he had a “dismal” handgun performance that would not improve with additional time and training.
The ruling comes after the Justice Department announced the results of a two-year civil rights investigation into the police department in Cleveland. They found officers arguably misused lethal force — including firing guns inappropriately.
The DOJ's report did not include the Rice case, and federal officials have said they will wait to initiate a formal investigation until after the local authorities have finished their inquiry.
The recent deaths have also inspired political action. On Friday, Rep. Emanuel Cleaver (D-Mo.) introduced legislation that would require all officers at state and local law enforcement agencies that receive federal money to wear body cameras.
President Obama has proposed funding the purchase of 50,000 new body cameras for officers nationwide.