MARINETTE, Wis. -- An Upper Peninsula man charged in a shooting rampage that killed three teenage swimmers at a river on the Wisconsin-Michigan border has been ordered to stand trial.

Scott J. Johnson of Kingsford, Mich., waived his right to a preliminary hearing during a brief court appearance Wednesday. A judge set a Sept. 5 hearing for the 38-year-old Johnson to enter a plea to three counts of first-degree intentional homicide.

Johnson is accused of emerging from woods on July 31 in camouflage and opening fire with an assault rifle on a group of young swimmers who had gathered at a river. Three were killed and another was wounded, all from Michigan.

A motive is not known.

Marinette County Chief Deputy Jerry Sauve said Johnson, who is from Iron Mountain, Mich., was arrested about 9 a.m. Aug. 1. Suave said he was still wearing camouflage as he walked out of some woods near the scene of the shooting and dropped his weapon as officers approached.

"We believe he was in the woods and near our officers who were also in the woods all night," Sauve said at a news conference.

More than 100 law enforcement officers from at least 10 agencies were called in to hunt for the gunman in Thursday's attack. Authorities had set up roadblocks and evacuated some homes in the northern Wisconsin area just across the state line from Michigan's Upper Peninsula. The shooting happened about 3 miles south of Iron Mountain.

Marinette County Sheriff Jim Kanikula said there was no communication between the gunman and his victims. The shooter was only 7 to 10 feet away from one victim when he fired on the group of nine young people who had gathered near a railroad bridge on the Menominee River, he said.

"There's a saying up here that this is a great place to raise kids," said Randy Van Gasse, the school superintendent in nearby Norway, Mich., where 17-year-old victim Tiffany Pohlson would have been a senior in the fall.

"That's been violated and we don't know why," he said. "This is obviously a shock to everybody."

The other dead were identified as Anthony Spigarelli, 18; and Bryan Mort, 19. A fourth victim, 20-year-old Daniel Louis Gordon, was wounded.