Almost nine months after four-year-old Gus Lamont vanished without a trace in South Australia’s remote outback, his grandmother is speaking publicly for the first time – and the unanswered questions remain as haunting as ever.

Gus disappeared from the family’s Oak Park Station near Yunta on September 27 last year, sparking one of the nation’s most baffling missing persons investigations.

Now, in an emotional interview with 7NEWS and Spotlight, Gus’ grandmother, Josie Murray, will open up about the painful toll the case has taken on her family.

Murray, who was interviewed by police during the investigation but never charged, says she still struggles to understand how the little boy could simply disappear. “We say ‘how, why’… we just can’t believe it,” she says.

She also speaks of the distress of being named as a key suspect during the investigation. “To be accused of doing something like this… you could not wish a more horrible experience on anyone.”

The special investigation, led by 7NEWS Adelaide crime reporter Hannah Foord and veteran journalist Michael Usher, promises to reveal fresh details and examine whether crucial clues may have been missed.

Police have carried out 11 searches of the vast outback property since Gus vanished, but despite months of work, the case remains unsolved.

In the interview, Murray also reflects on one moment from the day Gus disappeared that still troubles her. “There appeared to be something there,” she says.

Usher described the interview as potentially significant in the search for answers. “This is the interview that could provide answers to the many questions being asked about the disappearance of little Gus,” he said.

Australians will be able to watch the first part of the investigation on 7NEWS Adelaide this Sunday at 6pm, followed by the full interview on Spotlight at 8.40pm on Seven and 7plus.

Images: 7 News, SA Police