Brisbane mother Barbara McCulkin was allegedly strangled and buried in bushland with her girls.
This is one of the shocking revelations surrounding cold-case killings that have been revealed in a Queensland court.
In a bedroom conversation with his lover, Vincent O'Dempsey allegedly made a bombshell confession - he's a serial killer.
His former girlfriend says that four years ago the 70s underworld figure claimed he murdered 33 people.
"He said he was good for the McCulkin murders but they'd never get him for it," Kerri-Anne Scully told Brisbane Magistrates Court.
The horrific account of what allegedly happened to Barbara, Vicki and Leanne McCulkin came from Peter Hall.
He says he kept silent for decades, hiding a confession by Garry Dubois.
For 40 years police hunted for evidence like this.
The girls were separated from the mother, the court heard.
Vince allegedly took the mother away and strangled her and wanted Dubois to kill one of the children - but Dubois couldn't do it.
Dubois allegedly blamed O'Dempsey for all three murders in bushland near Warwick.
The men were friends of Billy McCulkin. The bodies of his wife and children are still missing.
Mr Hall said Dubois confessed to three friends and they all decided to never discuss it again. It was a pact that lasted decades.
Hall has indemnity from prosecution.
Now, he admits he and the accused men torched a Brisbane bar for insurance money.
Hall previously claimed Dubois had approached his gang, the so-called "Clockwork Orange Group", and told them O'Dempsey had commissioned them to stage an arson attack on the Torino's nightclub venue.
The group of four was paid $500 for the 1973 insurance con, given the night club "wasn't doing too well", he said.
A month later, Whisky Au Go Go was fire bombed, killing 15 people.
The court heard Barbara McCulkin believed her husband was involved in both fires and considered telling police.
Soon after, she was dead.
O'Dempsey, 76, and his co-accused, Dubois, 68, deny police allegations against them.
The hearing continues.