The death of a black man who was forced into a police car boot where a gas grenade was set off has sparked outrage in Brazil.
Police stopped Genivaldo de Jesus Santos, 38, in the street in the north-eastern city of Umbaúba, Sergipe state, on Wednesday.
Video footage showed two officers holding down the boot the man was in as thick smoke billowed from the car.
An autopsy report on Thursday confirmed Mr Santos died of asphyxiation.
Brazil's federal highway police said a disciplinary proceeding has been opened to investigate the officers' conduct. An investigation has also been opened by the federal police into the circumstances of Mr Santos' death.
There are conflicting reports of the incident.
A police statement said that Mr Santos had been arrested because he had "actively resisted" the police's approach, and that because of his "aggressiveness... immobilization techniques and instruments of less offensive potential" were used to restrain him.
But Mr Santos' nephew, Wallison de Jesus, told local media he had been at the scene, and his uncle had been riding a motorcycle when federal highway police officers stopped him and asked him to lift his shirt.
He said his uncle took prescription medication for schizophrenia, and got nervous when the officers found the medication.