New claims have emerged about a key piece of evidence that could help solve South Australia’s long-standing Beaumont Children mystery.

It has been revealed that a key suspect in the children’s disappearance was related to the family by marriage, potentially explaining why the children might have trusted him.

The Adelaide property that man once owned is now being excavated again by a private group.

”I think all of Australia want to see closure,” Independent MP Frank Pangallo said.

A fresh search got under way today in Adelaide’s Western Suburbs for the bodies of Jane, Arna and Grant Beaumont, who disappeared from Glenelg Beach in 1966.  

The privately organised dig is a last chance to see if anything can be unearthed at the former Castalloy factory site before a housing development is built on top. 

It’s land once owned by the deceased wealthy industrialist Harry Phipps.

The organisers of the dig believe he is the prime suspect in the disappearance of the three siblings.

The factory site was identified by two men, who were boys at the time and say they were paid to dig a grave-like hole there three days after the children disappeared.

The people who’ve been investigating Phipps believe he was a paedophile.

Today they revealed that just this week, a key new link between him and the Beaumont family has come to light.

Harry Phipps had a niece who married a cousin of Jim Beaumont, the children’s father.

There’s been a long-standing theory that the children knew their abductor they were seen playing with a mystery man at Glenelg and appear to have gone with him willingly.

“So we’ve been searching for that link, or that possible link, all that time, and now we’ve got one,” retired detective Bill Hayes said.

The excavation company is doing the work over the next week for free.

9News understands there was also an anonymous donation of $10,000 to help clear the site.

South Australia Police is not involved in this dig having previously said it did not believe it will succeed, but it is monitoring the outcome.