NIAGARA - A gunman suspected of opening fire on a group of young swimmers gathered along a riverbank was arrested Friday after he emerged from woods near the scene where three teenagers were slain and a fourth person was wounded.

Scott J. Johnson, 38, was dressed in camouflage when deputies confronted him following an all-night manhunt. He dropped his assault rifle as officers approached.

"We believe he was in the woods and near our officers who were also in the woods all night," said Jerry Sauve, chief deputy sheriff in Marinette County.

Nine young adults had gathered near a railroad bridge on the Menominee River when the gunman appeared late Thursday afternoon and opened fire, authorities said.

Investigators have not determined a motive. The sheriff said there was no communication between the gunman and his victims.

In another development, a judge in Michigan's Dickinson County on Friday signed a personal protection order against Johnson that was sought by a 24-year-old Kingsford, Mich., woman who claims he sexually assaulted her Wednesday after they went biking and then walked across the railroad bridge and into the woods in Wisconsin.

The order signed by Judge Mary B. Barglind prohibits Johnson from following the woman, appearing at her workplace or property or threatening her.

The woman told The Associated Press Friday night that she reported the sexual assault to police after telling her parents about it Wednesday night. She said officers came to her home Thursday night around midnight, mentioned the shootings and asked her to describe her attacker.

"I feel bad about those other people that got killed," she said. "It's scary. It could have been me."

Authorities did not return calls seeking comment on how the suspected assault might be related to the shootings or whether they were preparing any charges in the assault. The Associated Press does not name people alleging sexual assault unless they provide consent. The woman who accused Johnson did not want to be named.

About 250 people, many of them in their teens, turned out for a vigil Friday night at First Covenant Church in Iron Mountain, Mich.

Among them was 16-year-old Brittany Gunville, who said she was at the river with friends until about 15 minutes before the shootings. She said there were about 10 people playing around and swimming when her friend who drove had to leave.

"My friend had to work otherwise we would have still been there," she said as she and other young people hugged and consoled each other.

Johnson, from Iron Mountain, Mich., was being held in jail to await an initial court appearance. He had not been formally charged, and it was not immediately known whether he had an attorney.

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.

Sheriff Jim Kanikula said the shooter was only 7 to 10 feet from one victim when he fired.

"There's a saying up here that this is a great place to raise kids," said Randy Van Gasse, 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."

A woman who answered the door at a Kingsford, Mich., residence and identified herself as Johnson's mother said she was too distraught to speak with a reporter.

"They're not telling me nothing," she said tearfully. "I'm going crazy here. I wish they'd tell me something."

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

Spigarelli's aunt, Teresa Spigarelli, remembered her nephew as "spunky, sassy." She said he was cocky even when he was in fifth grade. She said he was handsome enough that he could have been a model.

Niagara, where a sign outside of town calls it "the city of scenic beauty," is about 210 miles north of Milwaukee. Across the Menominee River is Iron Mountain and Kingsford, Mich. The area is known for logging and tourism. The combined population of the cities is about 15,000.

(Copyright 2008 by The Associated Press. All Rights Reserved.)