Samaria Rice (C), the mother of Tamir Rice, the 12-year old boy who was fatally shot by police last month while carrying what turned out to be a replica toy gun, speaks surrounded by Benjamin Crump (L), Leonard Warner (2nd R) and Walter Madison (R) during a news conference at the Olivet Baptist Church in Cleveland, Ohio in this December 8, 2014, file photo.[Photo/Agencies]

The family renewed its demand for the US Justice Department to conduct "a real investigation" into the incident. Meanwhile, it filed a federal civil rights lawsuit against the officers involved and the city of Cleveland.

US police nationwide have long been accused of exercising racial discrimination in fighting crimes.

A total of 965 American civilians were shot and killed by US police in 2015, and unarmed black men were six times as likely as whites to be shot dead by police, a Washington Post report said Sunday.

Only 9 percent of the shootings, or 90 cases, involved unarmed civilians, but the victims were disproportionately black, according to the Post' analysis.

Although black men make up only 6 percent of the US population, they account for 40 percent, or 36, of the unarmed people shot to death by police in 2015.

The Post also found that a hugely disproportionate number -- three in five -- of those killed by police after exhibiting less threatening behavior were black or Hispanic.