Authorities in the central Montana city said the fatal shooting occurred after a 29-year-old man had been arrested Sunday on suspicion of burglary, after an hours-long standoff.
Police say the man was handcuffed in the back seat of an idling patrol car when he somehow climbed into the front seat and started driving.
Police Chief Rich St. John says the car hit Officer Dave Punt, who fired several shots. The car stopped after hitting other vehicles.
Paramedics performed CPR on the suspect and he was transported to a hospital, where he was pronounced dead. His name has not been released.