The arrest Friday morning ended a dragnet that included more than 100 law enforcement officers around the northern Wisconsin town of Niagara. Few details on the arrest, including the suspect's identity, were immediately released.
Nine young adults had gathered near a railroad bridge on the Menominee River when the gunman came out of the woods and opened fire Thursday with a military-style assault rifle, Marinette County Sheriff Jim Kanikula said. The gunman shot and killed three Michigan teenagers and wounded a 20-year-old Michigan man.
The river forms a border between Marinette County and Dickinson County in Michigan's Upper Peninsula.
No motive has been determined, according to the sheriff, who said there was no communication between the shooter and the young people. The shooter was 7 to 10 feet away from one victim when he fired, Kanikula said.
Tiffany Pohlson, 17, Anthony Spigarelli, 18, and Bryan Mort, 19, were killed, the sheriff said. Twenty-year-old Daniel Louis Gordon was wounded.
Pohlson attended Norway, Mich., High School where she would have been a senior this fall, said Randy Van Gasse, Norway-Vulcan Area Schools superintendent.
"Her personality and her smile will be missed," Van Gasse said.
He said the community was struggling with the tragedy.
"There's a saying up here that this is a great place to raise kids. That's been violated, and we don't know why," Van Gasse said. "This is a close-knit community. This is obviously a shock to everybody.
"This is where people come to relax and get away from craziness."
Officers had set up roadblocks at Highway 141 and county Highway N in Niagara and along some rural roads in Niagara as they searched for the gunman. Sheriff's deputies evacuated an unknown number of homes in the area.