A new dig will take place at an Adelaide factory in the search for the Beaumont children, who went missing in 1966, but SA police are not sure what they will find.
A three-metre deep hole dug at an Adelaide factory in 1966 is the focus of a renewed investigation into the disappearance of the Beaumont children but there's nothing to suggest it holds their remains, police say.
Major crime detectives will dig at the Plympton factory in coming weeks after a scientific assessment of the site revealed anomalies, indicating a large hole.
But they have also called for people to "temper their expectations".
"We don't know what we will find," Superintendent Des Bray told reporters on Tuesday.
"There's never been anything to prove that the Beaumont children are in the hole.
"However, common sense says, that even with the slightest chance that this hole could be relevant, we should search and that's what we're doing."
The factory first came to the attention of police in 2013 after two brothers told of digging a large hole at the request of then-owner Harry Phipps.
An excavation was conducted but nothing was found.
Mr Phipps has long been a person of interest in the disappearance of nine-year-old Jane, seven-year-old Arnna and four-year-old Grant who went missing on Australia Day 1966 after a trip to Glenelg Beach.
But Supt Bray said Mr Phipps, who was first investigated in 2007 and died in 2004, was not a suspect in the kidnapping and likely murder of the children.
"We've had hundreds of people nominated as a person of interest. We've had some of our most notorious and vile criminals from across the country nominated as suspects," he said.
"In some of them, we haven't been able to prove that they're responsible or exclude them.
"There's probably a list of 10 or a dozen people who fall into that category."
But Supt Bray said police believed the brothers were being truthful and their information warranted further checks, amid suggestions the 2013 dig had been conducted in the wrong spot.
"It's clear that the two men did dig a hole. It's never been in doubt. It's about where the hole was dug," he said.
The disappearance of the Beaumont children has been one of Australia's most enduring cold cases and subject to wild speculation at times, including possible sightings of the trio living as adults overseas.
A $1 million reward remains in place for information leading to an arrest and conviction or the discovery of the children's remains.
The parents of the Beaumont children have been told of the latest developments in the case.
Nancy and Jim Beaumont are now believed aged in their 90s and police are providing support to help them through "this difficult time", Supt Bray says.
"I just know that every time something comes up and there's speculation about it, it opens up old wounds and it's obviously a terribly difficult time for them on each occasion," Supt Bray told reporters on Tuesday.