A Milwaukee police officer who fatally shot a black man in August, sparking several nights of unrest on the city's north side, has been arrested on a sexual assault charge in an unrelated case, police said Thursday.

Officer Dominique Heaggan-Brown was arrested Wednesday, according to a statement released by the Milwaukee Police Department. The unidentified victim told police on Aug. 15 that Heaggan-Brown had sexually assaulted him while off duty, according to the statement.

The complaint was made two days after Heaggan-Brown fatally shot 23-year-old Sylville Smith, who police said was holding a gun when he was shot after a brief chase.

The department said an investigation found "additional allegations" that led to the charges against Heaggan-Brown. The criminal complaint wasn't publicly available Thursday morning, but the Milwaukee County Attorney's Office said it would be released later in the day.

Police said Heaggan-Brown is suspended and in custody, and they have launched an internal investigation. A police spokesman and the head of the Milwaukee police union didn't immediately return messages from the Associated Press seeking comment about the case.

Heaggan-Brown, 24, joined the police department in July 2010 as an aide. Like Smith, Heaggan-Brown is black. He was assigned to patrol the city's heavily minority north side.

Police Chief Edward Flynn has said that Smith was fleeing from a traffic stop when he was shot. Heaggan-Brown's body camera showed that Smith was shot after he turned toward an officer with a gun in his hand, according to investigators.

Smith's death sparked two nights of violence in the area's Sherman Park neighborhood, with several businesses burned. It also ramped up long-festering racial tension in Milwaukee.

The Wisconsin Department of Justice investigated Smith's death and has turned the case over to Milwaukee County District Attorney John Chisholm for a charging decision. It's not clear when a decision in that case will be made.