(CNN) A 21-year-old driver struggled with his passenger over the steering wheel before driving his truck into a group of Girl Scouts, killing three and one of their mothers, prosecutors in Wisconsin said.

The passenger told authorities he tried to correct the vehicle Saturday when he noticed Colten Treu crossing the center line near Lake Hallie, Chippewa County District Attorney Wade Newell said Monday.

Colten Treu

Treu was "somewhat out of it," the passenger said, and grabbed the wheel back, drove off the roadway and struck the group, Newell said.

A fourth girl, 10, was injured as the group was participating in a highway cleanup project. She was in stable condition Monday at a hospital.

Police have identified the victims as:

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