Harry Oakley, 45, of Speke, Liverpool, was discovered dead on Thursday in a block of flats in the city centre after he pursued eight to 10 youths who stole the cash dispenser from his bus.
He was found in a pool of blood and his death was initially being investigated by murder squad detectives but yesterday a post-mortem examination revealed that Mr Oakley, who was married with a 21-year-old daughter, had died of natural causes.
He had a cut to his head, believed to be caused as he collapsed on the third-floor landing. However, police are still treating his death as suspicious.
Police yesterday interviewed a 16-year-old about the incident. The chase occurred after a CMT Transport number 122 red bus had stopped in Byrom Street, in Liverpool city centre, at about 11am on Thursday, when youths jumped aboard.
They snatched the driver's cash dispenser and takings and fled, but he gave chase, leaving the double-decker unattended.
Police believe that Mr Oakley ran through nearby streets in pursuit of the gang and entered a block of flats in Juvenal Street, about 400 yards away.
Detective Chief Inspector Frank Thompson said: "He was found by a resident of the flats face down in a pool of blood on the third floor.
"Paramedics were called but he was dead when they got there."
Mr Oakley's widow, Audrey, said later: "It is hard to speak about what has happened. We're just hoping the police catch whoever committed this crime. My husband was a lovely man."
It is understood that the post-mortem examination revealed that Mr Oakley had scarring on his heart caused by a previously unknown condition.
Jeff Grant, a director of the firm Mr Oakley worked for, paid tribute to his heroism.
"It was typical of Harry to stand up for what he thought was right," he said.Reuse content