A man linked to the mysterious disappearance of the Beaumont children at an Adelaide beach in 1966 has died.
Allan "Max" McIntyre has reportedly died in a nursing home on the Yorke Peninsula west of Adelaide on Tuesday.
He was aged in his late 80s.
His son, Andrew McIntyre, recently broke his silence to Fairfax Media revealing his father and a family friend, Anthony Alan Munro, were at the Glenelg beach in the days around January 26, when Jane, Arnna and Grant Beaumont disappeared.
Munro is a former scout leader and convicted paedophile who will be sentenced in August for sexually abusing boys in 1965.
A child's diary that puts convicted paedophile Munro on Glenelg beach in the days surrounding the Beaumont children's disappearance there in January 1966 was recently handed to Adelaide detectives.
The "salvage and exploration club" diary was kept by one boy, and contributed to by another, tracking their adventures diving off the Adelaide coast that summer.
The dives regularly involved Mr McIntyre's father and family friend Munro.
Mr McIntyre, 63, was one of Munro's victims and a contributor to the diary.
Mr McIntyre says the diary is evidence that his father and Munro were frequenting Glenelg beach in the days before Jane, Arnna and Grant Beaumont went missing there on Australia Day 1966 in one of the country's most infamous mysteries.
The children were aged nine, seven and four when they took the bus from their nearby home to spend the day at Glenelg beach.
They were reported missing by their parents at 7.30pm, five hours after they were meant to return home.
Witnesses told police they had seen the children playing with a tall, blond man in his 30s.
The disappearance sparked one of the largest police investigations in the country's history.
In his statement to police as part of the investigation into Munro's abuse, Mr McIntyre alleged his father and Munro, now 72, were involved in the Beaumonts' disappearance.
"The day the Beaumont children disappeared was a shocking day in history that stands out in my memory very clearly," the statement, seen by Fairfax Media, reads.
"I believe Tony and Max were involved in the disappearance of the Beaumont children."
Mr McIntyre claims there was sand and blood in Munro's car on the day the children disappeared and believes his dad helped dispose of their bodies.
Max McIntyre, a former Telecom worker, was investigated over the disappearance after one of his daughters, Ruth Collins, made the allegations back in 2007 but police found no evidence he was involved.
The siblings have demanded that a filled-in well on their father's property outside of Adelaide be dug up, though the well remains undisturbed.