The victim was identified Monday as Daniel Brawley, 29, of Billings, who was taken into custody Sunday following an hours-long police standoff at a house where a burglary was reported.
After being placed in the back of the idling patrol car, Brawley somehow slipped out his plastic handcuffs, climbed over a partition into the front seat and attempted to flee, police said.
Police Officer Dave Punt was knocked down by the car but got up and fired nine times before the car crashed, authorities said.
Video taken by the news media showed people scrambling for cover as shots rang out in the neighborhood. The car stopped after hitting other vehicles.
"The cop started yelling at the car and it went straight at the officer," witness Brian Bersuch told The Billings Gazette. "It went by him and I heard about 10 or 12 rounds fire. I watched as that window just disintegrated in the back of the cop car."
Paramedics performed CPR on Brawley, and he was transported to a hospital, where he was pronounced dead.
Billings Police Chief Rich St. John said Brawley suffered a single gunshot wound to the torso. But it remained uncertain if he died as a result of being shot or from the crash.
Results of an autopsy were pending.
Under standard procedure, Punt was placed on administrative leave while the shooting is investigated. He was treated for minor injuries at a hospital and released.
St. John said the investigation would include a review of how Brawley slipped out of the handcuffs and got into the front seat. It will also determine whether officers including Punt acted appropriately during the standoff, Brawley's arrest, the attempted escape and the shooting.
The chief refused to speculate on whether Punt's use of deadly force was justified.
"I'm going to let the investigation play out. I'm not going to stand up here and Monday morning quarterback," he said.
Punt's patrol car was equipped with a video camera capable of recording actions in the back seat, but it was not turned on, St. John said.
Brawley had been due in state district court next week for a revocation of parole hearing stemming from a prior burglary conviction, police and court officials said. Further details on his criminal history were not immediately available.
Brawley's wife, Heather, also was arrested at the scene and charged with burglary. She was being held at the county jail.
Police received a call shortly before 9:30 a.m. Sunday when a woman reported a possible burglary at a house she was watching for someone who was out of town.
Responding officers spotted two people and at least one rifle and called in a SWAT team and a police negotiator.
After several hours, officers brought out the Brawleys, both handcuffed. They were placed in separate patrol cars.
Brian and Nancy Bersuch said they learned about the standoff while listening to a scanner and drove by the neighborhood on their way home from a store.
"They had the woman sitting on the front bumper of one of the new patrol cars," Brian Bersuch said. "They had the guy farther up the street and they put him in the back of that car."
Bersuch said he and his wife watched as an officer got into the front seat and then got out. He noticed somebody other than the officer was driving the car and yelled: "They're stealing your car!" Bersuch told the newspaper.
Another witness, Janielle Jacobson, told KULR the suspect was "laid over in the seat" by the time the patrol car hit a pickup truck across the street.