enough of it to definitively state that he had died of an overdose. Officially, the Clark County Coroner ruled that the boxer died of natural causes, specifically lung congestion and heart failure.

It was a verdict that - in the eyes of many boxing fans - only raised more questions. How could a man - still active as a professional fighter - suddenly drop dead? Was it possible that he could have been training while using hard drugs? And wasn't he afraid of needles anyway?

The strange circumstances of Liston's death - and the murky life he had been living at the time - have fuelled fierce speculation about what may have happened to him. Some, such as Sgt Caputo, accept the coroner's verdict of natural causes. But many stillstruggle to do so, and the prevailing theory - one that has only gained traction since his death - is that his criminal connections came back to bite him and he was murdered by the mob.

"The whole Liston story is so shrouded in mystery," says Rob Steen, who wrote a biography of the boxer. "There's so many people who died who might have been able to shed a little bit of light on it.

"But I don't think anyone ever really believed he had a heart attack."

Sonny Liston lost his heavyweight title to Muhammad Ali in a major upset in 1964

The mystery surrounding Liston's death is in some ways fitting. This is a man, after all, whose most basic details were the subject of speculation. He was born in