She said the names of the victims are expected to be released Monday by the Village of Lake Hallie Police Department.
Authorities say a 21-year-old man driving the pickup later surrendered.
Three girl scouts have been killed after they were hit by a truck while picking up litter. The girls were all wearing bright, lime-green safety vests so that they could be spotted by passing drivers.
Lake Hallie police said Monday Treu and a passenger in the pickup truck both told investigators they had intentionally been inhaling chemical vapours just prior to the crash.
The girls were fourth-graders and members of Troop 3055 in Chippewa Falls.
The head of Girl Scouts of the United States of America says "our hearts are broken" after three Girl Scouts and an adult were struck and killed in what authorities say was a hit-and-run crash along a rural Wisconsin highway.
Treu sped off from the scene but later turned himself in to police. The Chippewa County Sheriff's Office said that authorities are pursuing charges that would include four counts of homicide by negligent operation of a vehicle, four counts 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.
The Chippewa Falls Police Department expressed its condolences to the victims' families and fellow scouts, describing the events as a "truly horrific incident".
Another girl was injured and is in critical condition, the Lake Hallie Police Department said.
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Schafer was one of hundreds who gathered for a vigil outside Halmstad Elementary School in Chippewa Falls to pray for the vitcims.
"Our hearts are broken for the girls and families of the Girl Scouts of the Northwestern Great Lakes", Sylvia Acevedo, CEO of Girl Scouts of the US, said in a statement Sunday.
He will be charged with four counts of homicide, Lake Hallie police Sgt. Daniel Sokup said.
"We're going through a storm as girl scouts and as a community", said Chippewa Falls mother and former Girl Scout, Tricia Voigt.
In a message to parents, Superintendent Heidi Eliopoulos said: "This is a hard time for our students, families and staff".
Golden added the district and school crisis teams assembled support networks for students, staff and families.
Chippewa County DA Wade Newell claimed that Treu was impaired at the time of the accident, alleging that he was huffing from an air duster.
WEAU 13 News plans to bring you that news conference live on air, on our website, and on our Facebook page. At the time of the crash, all members of the group were in the ditch on the west side of County Road P just south of the Highway 29 overpass bridge. One girl died later at a hospital.