COLUMBIA COUNTY, Wis. — A criminal complaint alleges that a semi driver had been taking nearly twice the prescribed dosage of anti-anxiety medication before crashing into a school bus, the Milwaukee Journal Sentinel reports.

The complaint stated that on May 23, a HOPE Semper Christian Schools bus was headed to the Wisconsin Dells for a field trip when the semi crashed into the rear of the bus, according to the newspaper. The bus was parked on the shoulder of the road due to mechanical problems. Twenty people aboard were injured, four of them seriously.

Wayne Edward Murphy of Indianapolis, Indiana, a driver for Dahl Trucking, was “all over the road” before the crash, according to the complaint, and couldn’t tell deputies why the semi veered off the road before hitting the bus, Milwaukee Journal Sentinel reports. Murphy told deputies that he took one-and-a-half Sertraline pills about two-and-a-half hours before the crash, but the label on the pill bottle said to take one pill daily. The label also said that the medication can cause drowsiness and advised caution when operating a vehicle while consuming the medication. The complaint also said that deputies found a bottle of Xanax prescribed to Murphy in the semi, and determined he had taken about twice the prescribed dosage, according to the newspaper.

Murphy failed a field sobriety test before being taken to a hospital for a blood draw, the complaint stated, and was arrested for operating while intoxicated. According to the complaint and the Columbia County Sheriff's Office, Murphy was charged on Wednesday with five counts of injury by intoxicated use of a vehicle and five counts of second-degree reckless injury, Milwaukee Journal Sentinel reports.

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