Kowalczyk said it has been a challenging couple of days for his office, between investigating this case as well as the four deaths in a vehicle crash Saturday in Lake Hallie.
Defense attorney Kirby Harless asked for a smaller bond, saying the girl has lived her whole life in the area and there is no reason to think she wouldn't attend a future court hearing.
Monday morning, a cash bond was set at $250,000 for Treu.
Investigators say Treu and his roommate were huffing Dust-Off, a computer keyboard cleaner, Saturday morning while driving in Treu's truck.
Nine-year-old Jayna Kelley, 10-year-old Autum Helgeson, 10-year-old Haylee Hickle, and her mother, 32-year-old Sara Jo Schneider, were all killed in the tragedy.
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According to Fox News, Treu's vehicle veered into the ditch where the volunteers were picking up trash, and he drove off after hitting the victims.
The mother of one of the girls killed said she was standing near her daughter when the truck came crashing toward them.
The 21-year-old had nothing to say in court Tuesday, while appearing by video from the jail. The other girl was initially reported to be in critical condition. Authorities said Treu sped off after the collision, but surrendered hours later.
"She has to be treated as an adult", Newell said. Officials said she had been removed from the home of her biologial parents and was placed in a foster home.
The children were all fourth graders at Halmstad Elementary School and Southview Elementary School in nearby Chippewa Falls, about 145 kilometres east of Minneapolis.
"The child sustained head trauma and passed away November 1", Newell said.
According to the charges, deputies followed the fluid trail to a home in Chippewa Falls, which belonged to Treu and another man.