Robert "Bobby" Crimo III, the 22-year-old suspect of a mass shooting during an Independence Day parade in the Chicago suburb of Highland Park on Monday, had been "taken into custody without incident," said police during a brief news conference.
Highland Park is an affluent neighborhood 43 km north of Chicago.
The police gave no indication of the motive for the shooting that killed six and injured dozens.
The gunman used "a high-powered rifle," and fired from a rooftop, Sergeant Christopher Covelli from the Lake County Major Crime Task Force said at the news briefing. The rifle has been recovered at the scene.
Covelli called the crime "very random, very intentional."
Following the mass shooting, all Independence Day celebrations in Highland Park and the surrounding communities were cancelled.
