A 17-year-old boy was killed and four other people were critically injured when they were stabbed while tubing on the busy Apple River in Wisconsin on Saturday, law enforcement officials said.

The suspect, a 52-year-old man from Minnesota, had fled the scene but was taken into custody by police about an hour and a half after the incident began with the help of witnesses on the river. Authorities have not released the name of the suspect or the victim.

The victim who died was also from Minnesota, according to police, and the surviving victims were described as one woman and three men, all in their 20s. The suspect did not have a knife on him when he was taken into custody, and police are still looking for the weapon.

St. Croix County Sheriff Scott Knudson said investigators were not immediately clear on a motive for the attack but said the suspect and victims were tubing down the river in two separate groups when the incident happened.

“At this time we’re not sure what started this incident,” the sheriff said at a news conference Saturday. “It’s all believed that everybody was tubing.”

Knudsen described the scene as “scary” and “chaotic.”

“I’m sure that anybody that witnessed this will never forget it,” he said. “So it is a tragedy.”

The Apple River in Somerset, Wisconsin – a town about 35 miles outside of Minneapolis – is a popular for tubing and camping in the area. Resident Kat Fenton, who said she helped the father of one of the stabbing victims, told local outlet FOX 9 she was shocked by the stabbing at such a popular summer spot.

“I’ve never seen anything like this,” she said. “This is not OK. People just come here to have fun.”

Contributing: Mike Hart, The Milwaukee Journal Sentinel