Police investigating the Bradford City fire, which killed 56 football fans, knew who dropped the cigarette thought to have started the blaze, according to a new documentary.
A retired detective has told the BBC how officers worked out it was a man visiting from Australia called Eric Bennett who accidentally started the fire but a decision was taken at the time not to release his name.
The official inquiry into the tragedy on May 11 1985, headed by Sir Oliver Popplewell, concluded that it was an accident and was probably started by a spectator dropping a cigarette into rubbish that had accumulated under an old timber stand.
The blaze ripped through the wooden structure in just a few minutes as Bradford City played Lincoln City in an end-of-season match, leaving many fans unable to get out.
Retired Detective Inspector Raymond Falconer has told the BBC documentary - Missed Warnings: the Bradford City Fire - that he interviewed Mr Bennett.
Mr Falconer said: "He said he'd been at the match, he'd been sat in the stand, right where we knew the seat of the fire had taken place. He said he smoked a cigarette, dropped the cigarette onto the floor in front of him, went to put his foot on it, but it had unfortunately dropped through, he said, a knot hole."
The programme will show how an off duty police officer, who had been at the game, had been able to take photographs that pinpointed the place in the stand where the fire started.
Investigators reconstructed the seating area at a police station to work out who sat where.
The detectives eventually tracked down all the survivors apart from two men who had been visiting from Australia. One of them was Mr Bennett, who has since died. He had travelled from Australia with his nephew.
Mr Bennett told officers that he tried to extinguish the fire by pouring coffee onto it but, within minutes, smoke and then flames took hold.
Mr Falconer said: "They (the two men) rushed to the back of the stand. Got hold of some policemen. He told them what was happening. The policeman very quickly started to evacuate the stand. But the rest... Well, we know the tragic result of what happened. The truth is, that he dropped a cigarette and he was quite unequivocal about it. He'd dropped the cigarette that started the fire."
The retired officer said: " He was obviously troubled. And I felt extremely sorry for him. And this would be weighing on his mind for the rest of his life."
Relatives of Mr Bennett have confirmed many of the details of that day to the BBC but said he never told them he had dropped the cigarette that started the fire.
The documentary is being shown a day after more than 1,000 people gathered in Bradford city centre to mark the 30th anniversary of the tragedy.
Fifty-four Bradford City supporters lost their lives in the fire, along with two Lincoln City fans. More than 200 people were taken to hospital following the blaze, many with terrible injuries.
Relatives laid wreaths at the memorial in Centenary Square yesterday and stood in silence as the names of those who died were read out as the City Hall bell tolled.
The build-up to yesterday's anniversary has been overshadowed by a new book by Martin Fletcher, whose father, brother, uncle and grandfather died in the blaze, which claims that the fire was was one of nine that occurred at businesses owned or linked to the club's then chairman Stafford Heginbotham.
Since these claims emerged, there have been calls for police to reinvestigate the fire.
But Sir Oliver Popplewell, speaking to the BBC, said: "I think the conclusion that this was arson is mistaken.
"There's absolutely no need for another inquiry. I mean I think the police ought to have a look and get the fire authorities to have another look at these previous incidents and report. But I suspect they'll find nothing of any value."
:: Missed Warnings: The Bradford City Fire will shown on BBC One in Yorkshire and Lincolnshire tonight at 22.45pm and on BBC Two nationally at 23:20pm tomorrow.