He was identified as Scott Johnson, 38, of Iron Mountain, Mich., who was carrying a rifle and knife when captured, the Milwaukee Journal-Sentinel reported.
The three victims were identified as Tiffany Pohlson, 17, Anthony D. Spigarelli, 18, and Bryan Mort, 19. Daniel Louis Gordon, 20, also was shot but suffered only minor injuries, officers said.
A preliminary investigation revealed that the victims were shot about 5:30 p.m. Thursday while standing with a group near the East Kingsford railroad bridge on the Menominee River, about three miles west of Niagara, Wis. and 90 miles north of Green Bay.
"We are confident we have whoever we were looking for, the actor in this manner," said Jerry Sauve, chief deputy at the Marinette County Sheriff's Department, in a televised news conference. "We believe he was in the woods and near our officers who were in the woods all night."
He said no motive had been established.
More than 100 local and state law enforcement agencies, including the Wisconsin State Patrol and Michigan State Police, were involved in the overnight search.