Adelaide police digging at the potential gravesite of the Beaumont children have reached their "area of interest" after hours of excavation.
Australia is waiting with bated breath as police edge closer to finding out whether an Adelaide factory is the site of the remains of the siblings who went missing in 1966.
Metres of soil have now been removed and police have announced they are confident of reaching an "underground anomaly", which they detected using cutting-edge scanning technology.
Updating reporters at the site on Friday afternoon, Detective Chief Inspector Greg Hutchins said police had found nothing of interest, but would continue to dig around the western side of the site.
"We're now in the area of interest," he said. "If we break it up into two parts, on the eastern side we are right down about 2.8m, we're clearly into virgin soil and not finding anything at this point."
Insp Hutchins said officers were moving to the western side of the hole, where the dig "could take longer".
There was some excitement at the scene at about 1.30pm, four hours into the dig, when diggers discovered bones.
But police at the scene were quick to confirm evidence taken from the scene was not human bones — some animal remains had been found.
"We've found a number of non-human bones, they are from a large animal similar to a horse or a cow," Insp Hutchins said.
Following the discovery of the animal bones and "quite a bit of rubbish" on the western side of the site, Insp Hutchins said it was clear investigators were "now in disturbed soil".
The Adelaide Advertiser reported earlier police have begun removing small items found in the dig and securing them in evidence bags.
However police have since said they've discovered "nothing of interest" at the site.
Attention is focused on a small section of ground at the North Plympton site where recent scientific tests revealed the possible presence of a large hole dug there around the same time the three children went missing in 1966.
Detective Chief Inspector Greg Hutchins said there were innocent explanations for the anomaly those tests uncovered but it could also be a major breakthrough in Australia's most enduring cold case.
"We have our fingers crossed, we hope for the best but we do want to temper expectations," he told reporters at the site this morning.
"Clearly we have an anomaly which we need to investigate."
The dig, which as already gone on for over five hours, is expected to continue into the afternoon. Digging has began to slow now than top soil has been broken through and forensic investigators examine the site.
"At this point in time the intention is to keep going," Insp Hitchens told reporters just before 4pm. "I would hope in the next hour we should have a very good indication as to where we are at for the rest of the day."
Insp Hitchens said an officer was keeping Jim Beaumont - the missing children's father, no in his 90s - up to date.
Children never returned from the beach
The Beaumont children never returned after leaving their parents' Glenelg home for an afternoon at the beach on Australia Day, 1966.
Their disappearance sparked a wide-scale search operation, but Jane, 9, Arnna, 7, and Grant, 4, were never found.
In 2013, new information focused the investigation on a factory west of Adelaide, after two brothers told police they spent the 1966 Australia Day weekend digging a large hole there at the request of owner Harry Phipps.
Phipps died in 2004, but his son, who accused his father of years of sexual abuse, believed he had a part in the crime.
He also bore a resemblance to an identikit picture prepared at the time, and lived close to Glenelg Beach.
An initial excavation at the North Plympton site proved fruitless, but police now believe they may have been digging in the wrong spot.
Insp Hutchins said police had been in regular contact with the parents of the children, Jim and Nancy Beaumont, and had informed them of Friday's activity.
"Clearly the parents of the three Beaumont children have suffered significantly over the last 52 years," he said.
A range of experts are present at the site including a forensic anthropologist, a criminologist, crime scene examiners and officers from the major crime division.
The Beaumont children disappearance case sparked one of the largest police investigations in the country's history.
Clues as to what happened to the siblings have continued to surface since their disappearance from Glenelg Beach on Australia Day 1966, but leads have always led to dead ends.
Sightings of the children at Glenelg on the day they disappeared put them in the company of a tall, blond and thin-faced man with a suntan.
The investigation and the suspects
The Beaumont children's disappearance sparked a string of enormous investigations and saw detectives "inundated" with people trying to help find them.
Mostyn Matters was stationed at Glenelg in 1966 when the Beaumonts disappeared and says many people came forward at the time to help find them.
"We were inundated with people coming to give information," he told reporters at the Adelaide dig site on Friday.
"All we had was a little room at the front of the police station. We had one phone and people were queuing up to give statements.
"We only had a sergeant and four men there. We were snowed under."
That initial investigation and an intensive search operation provided no leads in what had become one of Australia's most enduring mysteries.
In late 2016, South Australian Police identified a 71-year-old former Adelaide scout leader as a person of interest in the mystery.
Millionaire bar owner and convicted paedophile Anthony Munro is in jail for unrelated child sex offences in South Australia dating back to 1962 — four years before the Beaumonts vanished.
Police interviewed Munro in June 2016 about Australia's greatest child abduction mystery after a child's diary said he was at Glenelg beach in the days surrounding the Beaumont children's disappearance.
The "salvage and exploration club" diary was kept by one boy, and contributed to by another, tracking their adventures diving off the Adelaide coast that summer.
Police have previously said there is no evidence linking Munro to the disappearance of the Beaumont children.
Another man who was linked to their deaths, Munro's friend Allan "Max" McIntyre, died in a nursing home on the Yorke Peninsula west of Adelaide June last year, aged in his late 80s.
His son, Andrew McIntyre, who was sexually abused by Munro, broke his silence last year revealing his father and Munro were frequenting Glenelg beach in the days around the disappearance of the three children.
Highly regarded detective Stanley Swaine, who died in 2002, was widely discredited following his retirement from the South Australian police force, but his obsession with the case continued well into his second career as a private investigator.
Mr Swaine led the case from 1967 when the Beaumont parents believed their children could still be alive.
He notoriously made an abortive trip with Jim Beaumont to Melbourne to investigate letters written by a person who claimed to know where the children were and that they were well-looked after.
In 1996, after the 30th anniversary of the children's disappearance, Mr Swaine made the outrageous claim that he had found a 40-year-old Canberra woman who was Jane Beaumont.
He said all three Beaumont children had been taken and raised by a satanic cult.
Weeks before he died, Mr Swaine made another claim about the Beaumont children to a journalist, saying he knew where they were buried and that a priest had told him it was in a church cemetery in Adelaide.