DEFOREST, Wis. (AP) — Columbia County's district attorney says she expects to file felony charges soon against the driver of a semi that struck a school bus and injured at least 20 people, including five critically.

DA Jane Kohlwey says the 42-year-old driver from Indianapolis had opioids and a tranquilizer in his system when he was arrested following the crash on Interstate 39/90/94 near DeForest on May 23.

The Wisconsin State Patrol says the semi struck the bus on the side of the interstate where it had pulled over due to mechanical issues. The State Journal reports Kohlwey says she expects to file charges of operating a motor vehicle under the influence and reckless endangerment.

The bus was carrying about 30 people from Hope Christian School in Milwaukee.

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Information from: Wisconsin State Journal, http://www.madison.com/wsj