The Carinthian man received a 15 year prison sentence for killing a Hungarian policeman by running him over with his Hummer in 2012.
It’s not clear why he suffered respiratory failure. There has been speculation that he committed suicide or was murdered in prison.
His lawyer, Janos Buza, told the Austrian Press Agency that he doubted that his client would have killed himself, and police have ruled out murder.
Buza said that his client, Thomas B, had been taking meals and exercising in the yard and that if he had intended to kill himself he would have been more likely to do it at night, rather than at 7.39pm.
He added that there was also a chance that his client’s sentence would be reduced in the near future.
There was also speculation that Thomas B might have taken a drug overdose but Buza said his client had only taken medication for toothache.