Peter Slatter was testifying at the inquest into the deaths of 15 people who succumbed to carbon monoxide poisoning after two drums of fuel were thrown into the downstairs foyer of the Fortitude Valley nightclub and set alight about 2am on March 8, 1973.
He spent hours with James Finch, one of two men convicted of the Whiskey attack, in a police interview room on March 11.
Asked about evidence already before the inquest that Finch confessed after being "touched up", Mr Slatter said he saw no sign of that.
"It didn't happen," he told the inquest in Brisbane on Tuesday when asked whether a confession was beaten out of Finch.
Mr Slatter said criminal lawyers in those days regularly accused police of verballing people to get confessions.
He also provided timelines he compiled from sources showing errors in timings provided by other witnesses.
Regarding one, referred to in the inquest only as Witness J, Mr Slatter said the best things he got right were his name, occupation and place of employment.
In response to questions from a legal representative for former police deputy commissioner Tony Murphy's wife, Mr Slatter said he never saw anything to suggest the senior officer was corrupt.
Mr Slatter confirmed he had always regarded the allegation Mr Murphy was involved in the Whiskey attack as "garbage".
Finch was "a bit aggro" when Mr Slatter first went into the interview room, but gradually calmed, the inquest was told earlier.
But Finch quickly pushed away coral trout given to him for lunch, saying he had hardly eaten anything since John Stuart - who was later convicted alongside him - told him 15 people had died.
"It's been on my mind ever since," Finch told Mr Slatter.
"You don't know how it feels. Fifteen bloody dead. Christ, I can't stop thinking about it."
Finch also claimed to have been living in the "bloody bush for days" with snakes, spiders and ants crawling over him since the firebombing.
Finch and Stuart, who have since died, were sentenced to life in prison over the attack.
Rumours have persisted that other people were involved and the inquest was reopened after the firebombing was mentioned in trials in which O'Dempsey and Garry Dubois were convicted over the deaths of Barbara McCulkin and her two daughters in January 1974.
Those trials heard the killings may have been motivated over fears Ms McCulkin would try to implicate O'Dempsey in the Whiskey attack.
Dubois was found dead in his Maryborough prison cell in June last year.
The inquest which is expected to hear from disgraced detective Roger Rogerson and O'Dempsey continues before coroner Terry Ryan.
