Decades-old diary holds chilling clue about the fate of missing Beaumont children.

Could a child’s diary from the 1960s hold the key to finally solving one of Australia’s most baffling mysteries?

It was a hot summer’s day in 1966 when the three Beaumont children vanished.

At 10am on January 26, nine-year-old Jane, six-year-old Arnna and four-year Grant said goodbye to their mother Nancy. They left their home in the Adelaide suburb of Somerton Park to catch a bus to Glenelg beach. It was a five-minute bus trip.

It wasn’t unusual for the children to go out on their own. Jane was considered a responsible child, and the three of them had been to the beach together the day before.

The children planned to be home by 2.30pm. When they hadn’t arrived by 7.30pm, their father Jim contacted the police. They searched the beach, but there was no trace of the children. They haven’t been seen since.

A shopkeeper at Glenelg remembers Jane buying pasties and a pie that day with a one-pound note, even though her mother hadn’t given her that much money. Witnesses saw the children playing with a tall, tanned, thin-faced man in this thirties with short blond hair.

The children were described by their parents as “shy”, so police theorised that perhaps they’d met this man on previous occasions. Arnna had mentioned to her mum that Jane had “got a boyfriend down the beach”, but her mum had thought she meant a playmate.

The disappearance of the children received massive publicity. Numerous sightings were reported, but none of the leads went anywhere. None of the children’s clothes or bags were ever found.

In November 1966, a Dutch psychic, Gerard Croiset, came to Australia to search for the children. He identified a site where he said they had been buried under concrete and a warehouse built on top. The public raised $40,000 to demolish the warehouse and excavate the site, but no trace of the children was found.

Two years after the disappearance, Jim and Nancy Beaumont received two letters supposedly written by Jane, saying a man was keeping them, and one supposedly written by the man himself. Police believed the letters from Jane could be real. The man said he was willing to hand back to the children to their parents, and nominated a meeting place. Jim and Nancy turned up, with a detective following them. They waited, but no one appeared.

Later, the parents received another letter, supposedly from Jane, saying the man had been willing to return them until he realised they’d brought a detective. Now, he was going to keep the children.

More than 20 years later, forensic testing showed the letters were fake. They were found to have been written by a 41-year-old man who was a teenager at the time. He claimed he’d done it as a joke.

For many years, the parents refused to move from their Somerton Park house. Nancy said it would be “dreadful” if the children came home and they weren’t there. The couple eventually separated. They no longer live in the house.

To police in South Australia, this is still an open case. On the 50^th anniversary of the children’s disappearance, Detective Superintendent Des Bray said they were still receiving, on average, a call every four days about the Beaumont children.

This latest lead comes from Andrew McIntyre. He says he and another boy kept a “salvage and exploration club” diary in the summer of 1965/66, where they wrote down their adventures diving off Adelaide beaches. Their dives often involved Andrew’s father, Allan “Max” McIntyre, and a family friend, Anthony Alan Munro.

Beaumont children's mystery 'blond' man could be found https://t.co/sagWtAivAl pic.twitter.com/yxLcYuRUbZ

— Billy Bloke (@eBayDownUnder) June 7, 2017

Munro is a convicted paedophile who lived in Glenelg in 1966. Andrew is one of his victims. Munro will be sentenced in August for abusing boys in 1965. Andrew claims his diary provides proof that his father and Munro spent time at Glenelg beach in the days before the Beaumont children went missing, and on the actual day.

Andrew made a statement to police as part of the investigation into Munro’s abuse. Fairfax Media has seen the statement, and it alleges that Andrew’s father and Munro were involved in the disappearance of the Beaumont children.

This isn’t the first time Max McIntyre has been linked to the disappearance. More than 10 years ago, his daughter, Ruth Collins, made allegations that he was involved. Police investigated but found no evidence to support her claim.

Last year, when Munro was arrested for abusing boys in 1965, he was questioned about the Beaumont children. The police found no evidence to suggest he was involved with their disappearance.

“Police have undertaken many actions and lines of inquiries in relation to this matter,” a police spokeswoman says. “There is no evidence at all to support these claims.”

In a statutory declaration, Andrew McIntyre says that on the day the Beaumont children disappeared, he was meant to go with his father and Munro to Glenelg beach. But he was told to stay home.

He claims that when the two men returned, both were upset. He claims there was sand and blood in Munro’s car.

Ruth Collins, meanwhile, claims her father had blood on his shirt when he came home. She also claims she saw the children's bodies in the back of the car.

The brother and sister are now asking for a filled-in well on their father’s property near Adelaide to be dug up.

More than 50 years after that hot summer’s day, the search for the Beaumont children continues.