Authorities in the United States have released the autopsy results of Tamir Rice, a 12-year-old boy who was shot and killed by a Cleveland police officer after he mistook a toy gun for a real one.

The Rice family has filed a wrongful death suit against the police claiming they used excessive force against their son.

Their case has now been bolstered by the judgment of a county coroner who has formally ruled that the boy's death is a homicide.

Tamir, who was black, was shot on November 22 by a white police officer responding to a call of a suspect waving a handgun around in a Cleveland park.

The weapon turned out to be a replica that typically fires plastic pellets. The sixth-grader died the next day.

The Cuyahoga County Medical Examiner's autopsy report said Tamir sustained a single wound to the left side of his abdomen that travelled from front to back and lodged in his pelvis.

The shooting came at a time of heightened national scrutiny of police use of force and two days before a grand jury declined to indict a white police officer in the August 9 fatal shooting of Michael Brown in Ferguson, Missouri.

Tamir Rice's family wants officers prosecuted over the boy's death. ( Reuters: Cleveland Police Department )

Tamir was shot less than two seconds after the police car pulled up beside him in the park, police have said.

They also released a security video of Tamir in the park before and during the shooting.

Tamir was 1.7 metres tall and weighed 88 kilograms, according to the autopsy report.

His mother, Samaria Rice, wants the officers to be convicted.

The family filed a lawsuit last week against the city of Cleveland and the two officers involved in Tamir's shooting, who are on administrative leave.

The officer who shot Tamir, Timothy Loehmann, had been on the Cleveland force for less than a year. A second officer, Frank Garmback, was driving the car. Both officers are white.

Cleveland's police force has been under a US Department of Justice investigation, which found in a report released on December 4 that the department systematically engages in excessive use of force.

The shooting of Tamir, and grand jury decisions not to indict officers in the deaths of Brown or a black man who was put in a chokehold during an arrest in New York, have driven protests over the police use of force in the United States.

This weekend Washington DC will host a mass rally to protest against the deaths of African-American men at the hands of police.



ABC/Reuters