Half a century ago on Tuesday, the three Beaumont children left their parents’ home in Adelaide for a day at Glenelg beach.

It was Australia Day 1966 and they were among hundreds, if not thousands, of people.

Yet they disappeared and have not been seen since.

Who took them and what their fate was has been the subject of intense police investigation, media scrutiny and public conjecture.

As the 50-year anniversary of that fateful day looms, it seems investigators are no closer to knowing exactly what happened to Jane, who was nine, seven-year-old Arnna and four-year-old Grant.

But as late as last week police began investigating another lead.

The case, they say, has not been and never will be closed.

“We had a phone call to the office from somebody who had been told something by somebody about who committed this offence,” Major Crime Detective Superintendent Des Bray told AAP this month.

“They firmly believed that the person they’re nominating has done it, so we’ve sent investigators to investigate those claims. That will take a few days to do.”

Whether that comes to anything, or whether it turns out to be just another dead end is yet to be seen.

And there have been hundreds of such tip-offs and leads.

Just in the past two years police have received 159 CrimeStoppers calls about the children, roughly one every four days.

Dozens of people are still considered persons of interest in the case but Bray says the window of investigation is closing.

Considering the passing of time, the person or persons responsible would now be aged between 70 and 100.

So the likelihood of any new information resulting in a breakthrough is slim at best.

One theory that has persisted over the years is a possible link between the Beaumont case and the disappearance of Joanne Ratcliffe, 11, and Kirste Gordon, 4, from Adelaide Oval in 1973.

The two children went missing during a football match after they went to the toilet.

Just like the Beaumonts, despite being surrounded by thousands of people, it seems no-one saw or heard anything, or at least anything suspicious.

And like the Beaumonts there have been thousands of leads investigated over the years, including one that prompted them to excavate a number of properties in SA’s mid-north in 2014.

Many people are convinced the same person who took the Beaumonts also took Gordon and Ratcliffe.

Police don’t discount a connection but have had nothing firm to go on.

In a new book on the Beaumont mystery, author Michael Madigan also delves into the Adelaide Oval disappearance.

And like many others, he describes the two cases as “carbon copies”.

“How could these two tragedies not be connected?” Madigan concludes.

Madigan also looks into the many scenarios and inquiries that have transpired in the search for the Beaumonts, from the use of a clairvoyant to the questioning of other known killers and pedophiles, including some who possibly ventured to Adelaide from interstate or were here as itinerant workers.

But he says one strong possibility is that the three children were abducted by a Glenelg resident.

“The simple task of inviting the children into a home for refreshments by the abductor would have looked safe to Jane, especially if that person was a young adult,” Madigan writes.

“It is quite possible that the precious souls of the three Beaumont children are buried at a Glenelg property, but where do you start digging?”

Short of a sudden or deathbed confession, we’ll probably never know.

– AAP