Milwaukee police say an officer shot and killed on the city’s south side was part of a unit that was conducting a search warrant on someone wanted for illegally selling firearms and drugs.

Officer Matthew Rittner was a tenured member of the department’s Tactical Enforcement Unit.

Sgt. Sheronda Grant said in a news release Wednesday night that Rittner and the other officers announced themselves as police and that the suspect fired several rounds. Grant said the 35-year-old Rittner was struck by gunfire and taken to a hospital, where he died.

She said a 26-year-old Milwaukee man was arrested. It wasn’t clear Wednesday night whether he has been charged.

Rittner, a veteran of the U.S. Marine Corps, began his career as a police aide in 2001.