(AP) — Authorities say a 27-year-old suburban Chicago man was killed when he fell out of a party bus and onto an expressway before he was struck by another vehicle.

Illinois State Police say the accident happened on the Tri-State Tollway near Deerfield early Saturday when James J. Larsen of Libertyville stood to change the radio volume.

Police say Larsen tumbled down the bus stairs and out the door. Master Sgt. Jerad Klint says Larsen then was hit by the other vehicle.

State police believe Larsen’s death was an accident and that he wasn’t pushed. Klint called it “a freak accident.” Police are looking for the driver of the other vehicle, which didn’t stop.

Investigators also are trying to determine if the party bus door was locked properly.

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