Both the man whose fatal shooting sparked violent protests in the US city of Milwaukee and the police officer who shot him are black, police said.
Chief Edward Flynn made the disclosure at a news conference on Sunday.
Mr Flynn identified the man killed on Saturday as 23-year-old Sylville K. Smith, and said Smith had a "lengthy arrest record".
Mayor Tom Barrett said a still image pulled from the officer's body camera shows "without question" that Smith had a gun in his hand when he was shot.
Police earlier said Smith fled from a traffic stop.
Mr Flynn said he was not sure what prompted the stop, but said Smith's car was "behaving suspiciously".
Smith's mother Mildred Haynes said he had a two-year-old son.
The Journal Sentinel reported Smith was charged last year in a shooting and was later charged with pressuring the victim to withdraw evidence that identified him as the gunman. Both felony charges were later dropped for reasons that are unclear.
Wisconsin governor Scott Walker has activated the state's National Guard to help law enforcement in Milwaukee if violence there persists.
At least four businesses were burned and one police officer was hurt on Saturday night in violence that broke out a few hours after the shooting.
Mr Walker says he took the step after receiving a request from Milwaukee County Sheriff David Clarke and talking with Mr Barrett and the Guard's leader. His announcement says the Guard will be in position to help "upon request".
Mr Walker praised citizens who showed up on Sunday to clean up the north-side neighbourhood where the violence took place.
He called for "continued peace and prayer".
The White House said President Barack Obama has been briefed on the outbreak of violence.
Spokeswoman Jen Friedman said Mr Obama was updated by senior adviser Valerie Jarrett. Ms Jarrett briefed the president after speaking with Mr Barrett and offering federal support for local authorities.