A special investigator says he "came out of the shadows" to warn police after being told the Whiskey Au Go Go nightclub would be burnt down before the fatal firebombing in 1973.
Former ACT attorney-general Bernard Collaery was also told now disgraced detective Roger Rogerson and another NSW police officer Fred Krahe were "jealous" of a heroin operation at the Fortitude Valley venue, the Coroners Court in Brisbane was told on Wednesday.
The former MP and prosecuted whistleblower - who was an investigator for the Immigration Department's Special Reports Branch in the early 1970s - was giving evidence by video-link at the inquest into the deaths of 15 people in the nightclub attack on March 8, 1973.
His team was told a woman had been recruited at the club as a drug mule and provided a passport by an immigration officer in Brisbane.
That officer admitted providing passports for people recruited at the venue to bring heroin from southeast Asia.
He also told Mr Collaery the Whiskey had attracted the attention of certain people in Sydney.
"I recall the immigration officer mentioning names I was familiar with, one of them was Roger Rogerson, and there was ... a police officer notoriously known as Freddy Krahe," Mr Collaery said.
"I recall knowing that those officers ... were involved in the antagonism towards the heroin trade that we believed was operating out of Whiskey Au Go Go."
Mr Collaery said Rogerson - who is expected to give evidence at the inquest on Friday - and Krahe were notorious in Sydney at the time for their corruption "and my team well knew it".
The officer also indicated threats had been made to stop the nightclub operating and that "there would be a fire".
Mr Collaery had no recollection of being told of any connection between the officers and the fire.
But the information was corroborated by a "well placed" Sydney-based informant Mr Collaery managed for years after he was detained for coming into Australia unlawfully.
The informant was so valuable his family was allowed into Australia legally "as a reward and to encourage that informant's deeper penetration into that world in Sydney at the time", Mr Collaery told the inquest.
He said attention had been brought previously to his team's work after they found a large heroin package that made him unhappy about becoming aware of the Whiskey's drug connection.
"There was a strong sense of national security in our work and it would not have been in the character of our activity to be involved in following up, in making accusations and turning ourselves into witnesses in this drug trade," he said.
But because of the serious nature of allegations the nightclub would be attacked with people inside Mr Collaery was instructed to pass on information to the head of Queensland's security branch.
"That was unusual, just to come out, because to be quite frank we didn't really trust the police,' he added.
Mr Collaery said his team came across allegations of violence or intended violence reasonably frequently.
"But the thing that made me raise this issue with my boss was that the club wasn't going to be burnt down at night, it was going to be burnt as a going concern," he said.
"That's why we sort of came out of the shadows."
He did not know how long before the firebombing he received the information.
Mr Collaery, a barrister, is accused of unlawfully sharing classified information about the alleged bugging operation of the East Timor prime minister by Australian officials in 2004.
James Finch and John Stuart were arrested within a week of the Whiskey bombing and convicted of murder that same year.
The inquest into the fire was re-opened following evidence in trials of Vincent O'Dempsey and Garry Dubois who were convicted of murdering Barbara McCulkin and her two daughters 44 years ago.
The inquest continues.
