(CNN) Three girls and a woman were killed Saturday morning when a truck driven by a Wisconsin man struck them as their Girl Scout troop was picking up trash along a roadway.

Another girl was injured and is in critical condition, the Lake Hallie Police Department said.

The driver of a black Ford F-150 "crossed over a lane of traffic and into the ditch, striking the Girl Scout troop," Sgt. Dan Sokup of the Lake Hallie Police Department told CNN affiliate WEAU

The driver fled, but turned himself in later. Police identified him as Colton Treu, 21, of Chippewa Falls.

"The Lake Hallie Police Department would like to extend our deepest sympathies to the families involved," police said in a statement.

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