A forensic expert is sifting through a two-metre-long "pit" discovered during the excavation of a site that is trying to establish whether the Beaumont children were buried there after they vanished in 1966.
Organisers of the dig, which began on Monday, say there is significant circumstantial evidence that Harry Phipps kidnapped, murdered and buried the three young children of Jim and Nancy Beaumont at his Castalloy foundry in suburban Adelaide.
Forensic archaeologist Maciej Henneberg said he was digging with a shovel and a trowel, excavating a 2m-long, 2m-deep pit of material that was in the initial area excavated on Monday.
"We are halfway through this, so I can't tell you yet whether there will be any other content besides," Professor Henneberg said on Thursday.
Dig organiser, independent MP Frank Pangallo, said "we're still going, we haven't given up" on solving Australia's most unsolved case.
"I now know what it's like to try and find a needle in a haystack," he said.
Since the dig at North Plympton began on Monday, more than 3000 cubic metres of soil has been excavated, in some areas up to a depth of 4m.
Jane, nine, Arnna, seven, and Grant, four, vanished without trace during a seaside outing to Glenelg 59 years ago.
In 2013, police excavated an area at the site after claims by two brothers that three days after the children disappeared, Mr Phipps paid them to dig a "grave-sized" hole on the factory site, which wil be sld for redevelopment when the dig is complete.
"We remain hopeful that we can find the hole that was dug by the two brothers," Mr Pangallo said.
"It's a mammoth job ... it's been enlightening being with Professor Henneberg and seeing how you actually do conduct a forensic dig for remains, this is how it should be done."
TV presenter Andrew Costello said if the search was unsuccessful, he would pay for an excavation at a second site at Stansbury on the Yorke Peninsula.
"There's some pretty full-on evidence that it is possible that the children could possibly have been buried in a sink hole on private property at Stansbury," he wrote on social media.
"My wife and I have decided that should the state wish and landowners agree, we will personally fund an excavation at the Stansbury site."
The search at the factory site will continue until Sunday.
