Vincent O'Dempsey has been found guilty of the McCulkin triple murder.

One of Queensland’s most notorious cold cases has been solved with a Brisbane jury finding Vincent O’Dempsey guilty of the 1974 murders of Barbara McCulkin and her two daughters.

The 78-year-old was convicted on Friday of all three killings after a four-week trial in the Brisbane Supreme Court, a little over a day after the jury hearing his case retired to consider its verdict.

Mrs McCulkin and her children Vicki, 13, and Leanne, 11, were taken from their Highgate Hill home on the night of January 16, 1974.

The trio was tied up and driven to bushland near Warwick where O’Dempsey is believed to have strangled the 34-year-old mother before killing the girls and burying their bodies.

O’Dempsey is the second man to be convicted over their deaths. His accomplice Garry “Shorty” Dubois, now 70, was last year found guilty of raping and murdering the sisters as well as Mrs McCulkin’s manslaughter.

Both men’s downfall came from their confessions to people they thought they could trust.

O’Dempsey, an underworld figure known as the “Angel of Death”, first opened up to associate Warren McDonald, who he was working with on a large cannabis crop in Carrara.

Mr McDonald told the trial they were driving to Warwick in 1997 when O’Dempsey boasted he killed the McCulkins but would never be charged.

“They’ll never catch me because they’ll never find the bodies,” O’Dempsey told Mr McDonald.

In 2011, Kerri Scully was engaged to O’Dempsey when he told her to buy the true crime book Shotgun and Standover from the local Big W.

While in bed, O’Dempsey showed her a picture in the book of himself walking from court with a leather jacket slung over his shoulder and bragged about the McCulkin murders.

“I’m good for it but they’ll never get me for it,” O’Dempsey said.

Ms Scully left the relationship the next day and remained in fear of the man who she later told police was an intelligent “serial killer” who covered his tracks.

“He takes you in the middle of the night, like an angel, and you’re gone for good,” Ms Scully told a committal hearing in November 2015.

The final key witness emerged just months before O’Dempsey’s trial – a remand prisoner, who cannot be identified, had noted down a confession on scrap pieces of paper and crosswords.

“She had to be dealt with,” O’Dempsey said.

“In those days you got paid to do a job, you did a job.

“I never laid a hand on the two kids, Shorty did.”

The informant also said O’Dempsey solicited him, once he was granted bail, to contact a person who would stop Ms Scully and Mr McDonald from giving evidence at the trial.

“He was trying to arrange to get at him (Mr McDonald),” the informant said.

“He knew what time he left for work, which road he took, which roadhouse he stopped at for breakfast … the number of his house.”

Dubois and O’Dempsey are expected to be sentenced on Thursday and will likely spend the last years of their lives behind bars.