BELLWOOD, Ill. (AP) — Investigators are trying to figure out why an ambulance driver in the Chicago suburb of Bellwood smashed the vehicle into a building with such force that it killed him, a co-worker and a patient.

Bellwood Mayor Andre Harvey says there is no indication the driver applied the brakes before the collision at about 3:45 p.m. Saturday. He says the ambulance was not involved in an emergency but was simply transporting the patient from a hospital to his residence when the crash occurred.

Harvey says an autopsy would be conducted to determine if the driver was suffering a medical emergency at the time of the collision.

The driver and the male patient were pronounced dead Saturday and a third man, an ambulance attendant, died at an area hospital early Sunday.