The parents of the Beaumont children “will never come forward” to speak about their private sorrow after a renewed search failed to find their children, according to the co-author of a book detailing Australia’s most famous cold case.

Police called off a dig at Adelaide’s New Castalloy factory for the remains of the missing children on Friday, uncovering only animal bones as they dug towards a detected anomaly around three metres below ground, but finding no sign of human remains.

Detective Chief Superintendent Des Bray told the media that nothing of interest to the investigation had been found and the latest search had been abandoned.

Alan Whiticker, who co-authored The Satin Man, told The New Daily that regardless of what happens, Jim and Nancy Beaumont are unlikely to speak to media after maintaining their silence for 52 years.

“They will never come forward because Mrs Beaumont is not well, but if something happened and it’s finally solved, Mr Beaumont would make a statement,” Mr Whiticker said.

“But never on camera again,” he added.

Jim and Nancy Beaumont, now 92 and 90 years old respectively, have not spoken to the media since 1968.

Major Crime Investigation Inspector Greg Hutchins said at a Friday press conference police were in regular contact with the Beaumonts.

SA Police called off a dig at an Adelaide factory after finding only non-human remains. Photo: AAP

The Satin Man, published in 2013, explored the disappearance of Jane, 9, Arnna, 7 and Grant, 4, who disappeared after a trip to Glenelg Beach on Australia Day in 1966.

The book’s title refers to “person of interest”, Harry Phipps, an Adelaide businessman known by friends and family for his sexual deviancy and his “satin fetish” who died in 2004.

The Satin Man details the mysterious disappearance of the Beaumont children.

Channel Seven named Mr Phipps a “potential suspect” in 2013 after his son Haydn said he had seen the children at his family home in Glenelg.

After living in hope their children might knock on the door of their home in Somerton Park, the Beaumont parents’ marriage ended in the early 1970s.

It’s widely reported the disappearance tore the Beaumonts’ relationship apart, but Mr Whiticker said the parents remain friends, still live in Glenelg and remain in constant contact with police.

Mr Beaumont lives in a unit in Glenelg with live-in care, while Mrs Beaumont resides in a nursing home.

“When I was writing my first book police warned me, don’t approach the parents, they don’t want to speak to you, so I respected their wishes and I didn’t want to add to their pain,” Mr Whiticker said.

The author said the Beaumont children mystery was a rare case and the Australian public “turned on them” when there were no easy answers to explain the disappearance.

In one episode that perhaps clinched their silence, Mr Whiticker said an anonymous letter was sent to the Beaumonts’ home asking them to come to Dandenong in Melbourne to be reunited with their children.

It was later revealed a 16-year-old boy had penned the letter and was charged on misdemeanour, but the Beaumonts were traumatised by the cruel hoax and “media circus”.

“[The Beaumonts] are wonderful people, but they’ve been badly treated by not only sections of the media, but sections of the public,” Mr Whiticker said.

“They’ve borne more than anyone could understand.”