(CNN) The man police say was driving a truck that killed three Girl Scouts and a woman in Wisconsin had been "huffing," or intentionally inhaling chemical fumes, police said Monday.

Colten Treu

The woman was the mother of one of the girls killed Saturday, police said.

Colten R. Treu, 21, drove his pickup truck into the group of Scouts , the Lake Hallie Police Department said. The girls were wearing highly visible green safety vests while participating in a highway cleanup project.

Treu's bond was set at $250,000. He was due back in court Tuesday.

The Chippewa County Sheriff's Office said he is being held on four counts of homicide by negligent operation of a vehicle, four counts of homicide by intoxicated use of a vehicle, four counts of hit-and-run involving death and one count of hit-and-run involving great bodily harm.

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