Driver jailed on suspicion of being intoxicated in crash that killed 3 Wisconsin Girl Scouts and an adult picking up highway trash: Jail official

As a community mourned three Girl Scouts and an adult supervisor who were killed when a pickup truck struck them as they were picking up trash alongside a Wisconsin highway, the suspected driver was in custody Sunday on suspicion of being intoxicated when he allegedly ran them over, officials said.

The suspect, Colten Treu, 21, is expected to appear in court on Monday, officials said.

He was being held in jail on suspicion of homicide by intoxicated use of a vehicle and homicide by negligent use of a vehicle, an official at the Chippewa County Jail in Chippewa Falls, Wisconsin, told ABC News on Sunday. He graduated from a school within the Chippewa Falls Area Unified School District, Superintendent Dr. Heidi Eliopolous told reporters Sunday afternoon.

Eliopolous, who lives near the highway where the victims were struck, first saw the emergency response vehicles and then was informed by a neighbor that "younger children were involved" in the accident.

"And our instincts kicked in, knowing that if there was an accident in our community, there was a very good chance it was our students," she said.

Two of the students who were killed attended Halmstead Elementary School, while the third student attended Southview Elementary School, Eliopolous said, adding that the adult supervisor who was killed was the mother of the Southview student.

The names of those killed will be released Monday, Eliopolous said.

Local residents were planning to hold a candlelight vigil for the victims Sunday night at Halmstad Elementary School in Chippewa Falls, where the three girls were all in the fourth grade.

A fourth Girl Scout struck by the truck remained in the hospital Sunday in critical condition, officials said. She attends Halmstead Elementary, Eliopolous said.

"Our hearts are broken for the girls and families of the Girl Scouts of the Northwestern Great Lakes," Sylvia Acevedo, the chief executive officer of the Girl Scouts of the USA, said in a statement Sunday to ABC News. "The Girl Scout movement everywhere stands with our sister Girl Scouts in Wisconsin to grieve and comfort one another in the wake of this terrible tragedy."

The girls were picking up garbage at 11:41 a.m. on Saturday near the village of Lake Hallie, about 95 miles east of Minneapolis, Minnesota, when a Ford F-150 pickup truck allegedly driven by Treu veered off a roadway and into the ditch, striking the four girls and an adult who was overseeing their volunteer work, said Sgt. Daniel Sokup of the Lake Hallie Police Department.

Treu allegedly left the scene after hitting the group, Sokup said. Treu surrendered to police Saturday night and was placed under arrest, Sokup said.

It was not immediately clear whether Treu had retained an attorney.

The incident came at the end of a particularly deadly week for children hit by cars throughout the U.S.

In another deadly crash, three siblings died when they were hit by a pickup truck while boarding a bus in Rochester, Indiana, on Tuesday.

A 9-year-old boy was struck and killed while crossing the street to board a bus in northern Mississippi on Wednesday, and a second-grader in Pennsylvania was killed when struck by a vehicle at a bus stop on Thursday.

Five children and two adults were struck by a car at a bus stop in Tampa, Florida, on Thursday as well, though none of the injuries were considering life-threatening.

The school district is providing counseling and therapy dogs in the aftermath of the tragedy, Eliopolous said.

"This is a difficult time for our students, our families and our staff," she said. "We’ll provide ongoing support as long as it’s needed."

In a joint statement, Halmstead Elementary School Principal Wade Pilloud and Southview Elementary School Principal Sara Denure thanked the community for the "outpouring of support."

"Please join us by continuing to support our grieving families with your thoughts and prayers," the statement read. "We have received an overwhelming outpouring of support from our community, from around the state and from around the nation."

ABC News' Julia Jacobo contributed to this report.