Colour television was still a year away, a loaf of bread cost 24 cents, Gough Whitlam was Australia's Prime Minister and Sir Joh Bjelke-Petersen ruled Queensland.

And on the humid night of January 16, 34-year-old Barbara McCulkin and her daughters Vicki, 13, and Leanne, 11, vanished from their modest home in Brisbane's inner-south, sparking one of Queensland's most enduring mysteries.

For four long decades, the families of Barbara, Vicki and Leanne McCulkin have patiently waited for closure.

Finally, on Saturday, it came a step closer.

Cold case and homicide detectives swooped on the homes of long-time suspects Vincent O'Dempsey and Gary Dubois early in the morning, later charging each with the trio's abduction and murder.

While at pains to stress it is just the first step in a potentially long prosecution process, homicide Detective Superintendent Steve Holahan said Ms McCulkin's family was "very appreciative" the matter had progressed to the point of charges being laid.

The arrests of O'Dempsey, 76, and Dubois, 67, come nearly 35 years after prosecutors were forced to drop murder charges against the pair due to a lack of evidence.

This time, however, Superintendent Holahan said, fresh evidence gathered following the reopening of the investigation on the 40^th anniversary of the McCulkin's disappearance in January had bolstered the case.

Each man is charged with three counts of murder and three counts of deprivation of liberty, among a litany of charges.

Both are scheduled to front Brisbane Magistrates Court on Monday.

It is the latest development in a forty-year mystery that has long intrigued Brisbane.

The day after Mrs McCulkin and her two young daughters vanished from their home in Highgate Hill, the home appeared simply abandoned – lights on, windows open and sewing sitting unfinished on a machine.

Witnesses placed two men in the house the night the trio disappeared and from early on investigators theorised they were dealing with a triple murder, though bodies have never been found.

The most enduring theory as to motive was that Barbara had vital evidence that would implicate the perpetrators of the Whiskey Au Go Go nightclub firebombing 10 months earlier that killed 15 people.

Until the Port Arthur massacre in 1996, it was Australia's worst mass killing.

But despite the tantalising gangland link, in announcing the reopening of the investigation in January, Cold Case Detective Acting Superintendent Mick Dowie said new information suggested the motive was far less high-profile.

It took the investigation in a new direction.

"We have spoken to someone who has probably caused us ... to put aside all the scandal and association of this murder with all the other criminal activity that was occurring back at the time," he said.

Yet the two men charged on Saturday remained persons of interest in the investigation, Superintendent Holahan said on Saturday.

He said new evidence that emerged following the reopening of the case this year would form a key component of the prosecution's case.

"In saying that, however, we will be relying on a substantial amount of evidence gathered in previous investigations and the coronial investigation," he said.

The detective said that, while the 40-year-old resting place of the mother and her two daughters was still unknown, his investigative team would not give up the hunt.

"We won't give up ever on that, if any information comes in we will certainly act on it," he said.

On Sunday, Queensland Premier Campbell Newman congratulated police on the investigation.

"For the McCulkin family, the extended family and friends, this must be a very positive thing for them (after) 40 years of uncertainty," he said.

The probe was a joint investigation between homicide and cold case detectives and of hearings undertaken by the Crime and Corruption Commission this year, the coercive powers of which Superintendent Holahan credited as providing crucial new evidence.

Anyone with information is asked to contact CrimeStoppers on 1800 333 000 or crimestoppers.com.au.

- with Amy Remeikis