TRUE CRIME: Barbara McCulkin and her daughters were murdered because they knew too much.

It was 1974 and Barbara McCulkin was looking forward to a fresh start.

She’d just undergone surgery to remove the stretch marks from her stomach and breasts. Her husband Billy McCulkin – a violent drunk who regularly associated with criminals – was moving in with another woman and Barbara and her two daughters were finally free.

Free from the trope of criminals that had been flowing in and out of their Queensland home, muttering about fire bombings and vandalism attacks. Free from the speculation – the fact she knew her husband, a small time gangster, had played a role in the tragic fire at the nightclub Whisky au Go Go in Brisbane a year earlier.

The arson had claimed the lives of 15 innocent people and two of Billy’s mates – John Andrew Stuart and James Finch – had been found guilty for the murders.

It had been the trigger to make her leave – only 36 hours after the nightclub bombings and Barbara had moved out of her home and into a friend’s house. She had told her neighbour Peter Nisbet that her husband “had something to do with the Whiskey Au Go Go fire”.

“Barbara indicated that Finch and Stuart were not the primary movers of the Whiskey and that they were just collateral damage or an easy get for the cops,” Nisbet told police. “She seemed to think Stuart was set up for the Whiskey Au Go Go fire.”

Nisbet wasn’t the only person Barbara confided in and, months later, they were all dead. Barbara and her daughters, 13-year-old Vicki McCulkin and 11-year-old Leanne, disappeared without a trace on January 16, 1974.

Why? She knew too much.

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She had been present when Billy’s gang – called ‘Clockwork Orange’ that involved himself, as well as break-and-enter criminal Vincent O’Dempsey and rapist Garry Dubois – had been planning the Whiskey au Go Go bombings in her kitchen.

“The flames burst through the front door and lit the curtains all the way up to the ceiling” Donna Phillips, whiskey waitress, told Channel Seven’s Sunday Night this evening. “I watched [another bartender] catch alight, I watched him run around the bar with his shirt burning and then fall to the ground. I watched him die.”

Fifteen dead bodies were laid out in the nightclub’s car park the following morning and, soon enough, Barbara knew the wrong men had been put away.

“She could actually absolve Stuart and Finch of their responsibility,” security guard John Ryan told Sunday Night. He said Barbara’s plan had been to tell her story, put her husband behind bars – where he could no longer hurt her – and run away.

She postponed reporting it, so her daughters could attend a birthday party.

Fifteen people died inside the Whiskey Au Go Go nightclub. Former constable Hunter Nicol still can’t forget the horror. pic.twitter.com/WigLW9IoUO

— sunday night (@sundaynighton7) May 28, 2017

The afternoon of Wednesday January 16, 1974 was unremarkable. Barbara and her daughters Vicki and Leanne were back at the family home. Billy had moved out and the girls had been invited across the road to the neighbour’s – the Gayton’s – house for their friend’s birthday celebrations.

While they were there – eating cake and being 14 and 11 year old girls – their mother welcomed an unexpected O’Dempsey and Duboi into her home.

Later, when the Gaytons watched the two girls return across the road to their mother, they didn’t realise it would be the last time anyone ever saw of the McCulkin women.

When Billy called around to the house two days later, he could not find his wife or daughters.

He broke the glass in the front door and found no one had slept in their beds. Nothing was missing. His daughter's 'Wednesday' outfits were out of their cupboard, and Wednesday was two days ago.

He knew something was wrong and, after quizzing the neighbours, who had been told by Vicki and Leanne of O'Dempsey and Duboi's visit, he was extremely concerned for his family's welfare.

He knew O'Dempsey, especially, was capable of murder.

Billy, for his sins, would never give up on the search for his ex-wife and daughters. He went to the police, reported his wife and daughters missing, and even shared his conviction that O'Dempsey and Duboi were behind it.

No bodies were found. No blood or signs of a struggle were found. It was a dead-end and Billy died in 2011, never seeing justice.

“Was Vincent O’Dempsey the sort of man who could murder a mother and her 2 daughters? “Oh, absolutely.’ #SN7 pic.twitter.com/kwefIpijyR

— sunday night (@sundaynighton7) May 28, 2017

Only this week, after the testimony of former 'Clockwork Orange' member Peter Hall as well as three other key witnesses, was O'Dempsey found guilty of the murder of Barbara, Vicki and Leanne.

In November last year, his accomplice Duboi was also convicted of the rape and murder of siblings Vicki and Leanne and the manslaughter of Barbara.

“[Duboi] told us they took the girls for a drive,” Hall said in his statement. The rapist-come-murderer had confided in him years earlier.

"Duboi said he didn’t know what was in O’Dempsey’s head at first, but Vince tied them up. He said he drove them to the bush and that’s where it happened."

“He said Vince took Barbara away into the dark and strangled her. He said that Barbara was not raped; he thought that’s what it was going to be but he just killed her."

O’Dempsey raped one of the children and Dubois raped the other. "He didn’t say specifically how the girls were killed but he was clear he didn’t kill anyone. Vince killed them all," Hall said.

Still, the bodies have never been found.

"Be man enough to tell us where the bodies are so the families can have some finalisation," police officer Alan Marshall told Sunday Night.

Billy McCulkin went to his grave, "not knowing why he didn't kill O'Dempsey and Duboi, himself," he said.