A former private eye says a Brisbane mother and her daughters vanished soon after she had asked him to move them to a safe house.

A former private investigator says he was about to move Brisbane mother Barbara McCulkin to a safehouse when she and her young daughters vanished from their home 40 years ago.

Police believe they could be close to cracking the suspected murders of Mrs McCulkin and her daughters, Vicki, 13, and Leanne, 11, who were last seen at their Highgate Hill home in January 1974.

The renewed investigation is focused on persons of interest who were identified in the initial police probe and a 1980 coroner’s inquest.

That inquest saw two men, Vincent O’Dempsey and his associate Gary Dubois, charged with the McCulkin murders, but the charges were later dropped due to a lack of evidence.

Former Brisbane investigator John Ryan has told The Brisbane Times he was going to take Mrs McCulkin and her daughters to a safe house near Glen Innes, in NSW.

But when he arrived at the family’s Highgate Hill home, he learnt the mother and her daughters had disappeared.

“She (Mrs McCulkin) rang me the night before and wanted me to get her to a safehouse,” said Mr Ryan.

“I knew she was dead.”

He said he’d taken notes at the time about everything Mrs McCulkin had told him before she vanished, and was interviewed in January by police who are re-examining the crime.

Mr Ryan believes she was murdered before she could speak out about what she knew about the bombings of the Torino’s and Whiskey Au Go Go nightclubs in Brisbane’s Fortitude Valley.

Torino’s was attacked in February 1973, the month before the Whiskey Au Go Go was firebombed, killing 15 people.

Mrs McCulkin’s husband, Billy McCulkin, was a debt collector linked to underworld figures.

At one stage, McCulkin was charged over the Torino’s attack but those charges were withdrawn after prosecutors decided there was no prospect of a conviction on the available evidence.

In late 1973 and early 1974, after her husband left her for another woman, Mrs McCulkin had reportedly been drinking too much and was regularly heard in Brisbane bars threatening to reveal what she knew.

“Barbara knew what happened and was murdered because she had threatened to talk,” said Mr Ryan.

“She knew everything because so much of it was arranged in her house.”

James Richard Finch, 29, and John Andrew Stuart, 33, were convicted of the March 1973 Whiskey Au Go Go fire bombings in October 1973.

Police this week raided three rural properties as they continue to work on the McCulkin case, and drug trafficking charges have been laid against one man as a result of those raids.

Thomas Edward Martin was charged after a raid at a rural property at Warwick, in Queensland’s Southern Downs, on Wednesday, which netted $300,000 in cash and 50kg in cannabis.

Police believe Martin has close links to Vincent O’Dempsey, one of the two long-time persons of interest in the McCulkin case, but say he is not suspected of being behind those deaths.

Officers have also said Mr O’Dempsey is not suspected of involvement in the drugs find.

The coronial inquest into the McCulkin disappearances found no evidence that Billy McCulkin, who is now deceased, was involved.