The Marinette County sheriff's department say it doesn't know why a Michigan man dressed in camouflage shot and killed three young people along the state border.

Authorities arrested 38-year-old Scott Johnson from Iron Mountain, Mich., Friday morning in the area where the victims were shot Thursday.

Chief Deputy Jerry Sauve says Johnson complied with officers' orders to throw down his assault rifle as they arrested him in a wooded area in the Town of Niagara. Sauve says Johnson was also carrying a knife. He has not been charged in the case.

A team of more than 100 law enforcement officers from various agencies had searched through the night for the gunman.

Marinette County's sheriff says the shooting that left three young people dead and another wounded was apparently a random act.

Sheriff Jim Kanikula says a man dressed in camouflage and armed with an assault rifle came out of the woods and started shooting. The sheriff says there was no communication from the gunman with the group of nine young people who had gathered at a Menominee River bridge to swim.

Kanikula says the shooter was seven to ten feet away from one of the victims when he fired.

17-year-old Tiffany Pohlson, 18-year-old Anthony Spigarelli and 19-year-old Bryan Mort were killed. 20-year-old Daniel Louis Gordon was wounded. All were from Michigan.

Roadblocks were set up in the area and some homes were evacuated as authorities searched for the gunman.

Sauve says the call came in at about 6 p.m. Thursday night of a shooting in the town of Niagara. That's in the far northern part of the county along the river.

Sauve called it an "active shooter situation," with all available personnel from his department and others in the area out investigating, with the aid of air support.