John Bargenquast - who was charged over stolen vehicles and thought his family would be arrested too - asked the police minister's press secretary to pass on a message to senior officers, the ministerial aide's two sons told the Coroners Court in Brisbane on Friday.

Christopher and Graham McGetrick, friends of Mr Bargenquast's children, gave evidence into the attack on the Brisbane nightclub that killed 15 people.

Christopher McGetrick, a former journalist, said he thought it was in 1979 when his father told him Mr Bargenquast had asked for a favour the previous day.

"He said to my dad in general terms, 'Look, I'll cop it myself, I'll do the time, but I just do not want to see my family brought into this'," Mr McGetrick said.

Mr Bargenquast asked the aide to pass on a message to then police deputy commissioner Tony Murphy.

"Basically the message was that, 'let Murphy know if the charges against my family are not withdrawn then I will blow the lid on the Whiskey Au Go Go', essentially words to that effect," Mr McGetrick said.

He told the inquest his father let him know Mr Murphy became quite aggressive when approached at a police function and asked about his involvement with "that bastard" referring to Mr Bargenquast.

Mr McGetrick said his father told him Mr Murphy spoke to police commissioner Terry Lewis, then returned, saying they wouldn't be intimidated and were calling Mr Bargenquast's bluff.

Mr Bargenquast later thanked Mr McGetrick's father for his help, saying the charges against his family had been dropped.

Mr McGetrick said he spoke to Mr Bargenquast about the incident and the stolen car racket on his release from prison at a family event.

The former journalist said he believed Mr Bargenquast had evidence about the Whiskey attack, but had no knowledge of what that evidence might be.

Brother Graham McGetrick told the inquest he was living with his parents when Mr Bargenquast visited, but thought his father was asked to speak to Mr Lewis.

"I knew he was going to see the hierarchy and, look, I was pretty sure it was Terry Lewis. I could have got that wrong, but I was pretty sure it was," he added.

Graham McGetrick said he understood his father was asked to pass on a message that the lid would be blown off the Whiskey Au Go Go if the charges against Mr Bargenquast's family were not dropped.

Two drums of fuel were thrown into the downstairs foyer of the Fortitude Valley nightclub and set alight about 2am on March 8.

Two men - John Andrew Stuart and James Richard Finch - were convicted in 1973 of murder over the attack and sentenced to life in prison.

Both men have since died.

The new inquest was ordered after the firebombing was mentioned in a trial in which Vincent O'Dempsey and Garry Dubois were convicted over the deaths of Barbara McCulkin and her daughters.

That trial was told the killings may have been motivated over fears Ms McCulkin would try to implicate O'Dempsey in the firebombing.

O'Dempsey - who has sat in the court during some testimony - is expected to testify during the last week of the sitting.

Dubois was scheduled to give evidence, but was found dead in his cell at Maryborough Correctional Centre last year.

Australian Associated Press