A sex assault suspect who suffered critical injuries in the back seat of a Metro Transit squad car in downtown Minneapolis over the weekend intentionally set himself on fire with a cigarette lighter, according to a Minneapolis Fire Department report.

The incident occurred late Sunday morning after transit police answered a call about a woman being assaulted on the U.S. Bank Stadium light-rail platform, according to emergency dispatch audio.

The 31-year-old man from St. Cloud was taken to HCMC in critical condition. Transit police released his name, but the Star Tribune generally does not identify suspects before they are charged.

Neither Metro Transit nor the state Bureau of Criminal Apprehension, which is leading the investigation, has said why the suspect had the lighter after he was arrested on suspicion of trying to sexually assault the 34-year-old woman in what police called a stranger attack.

Metro Transit policy says officers should "remove all weapons, dangerous items and contraband" when taking someone into custody.

Transit spokesman Howie Padilla declined to say whether a lighter would be among those confiscated items.

Police did say the man had only one arm but did not address whether that disability affected their ability to handcuff or otherwise restrain him.

The Fire Department said the skin on the man's torso was burned.

"The patient lit his clothes on fire with a lighter while in back of the police car," the report continued.

A Metro Transit officer suffered minor burns from pulling the man out of his squad car.