The grandmother of missing boy Gus Lamont will speak for the first time as the mysterious case of the four-year-old who vanished without a trace in the South Australian outback continues to baffle investigators.

A major joint investigation by 7NEWS Adelaide and Spotlight is set to reveal new details about what may have happened to the little boy.

Gus’ grandmother Josie Murray will speak for the first time, asking how the four-year-old disappeared in the remote outback at the family’s Oak Park Station near Yunta on September 27 last year.

Murray, a central figure in the investigation into Gus’ disappearance, reveals the toll of the past nine months, including the pain of being identified as a key suspect and the moment that still troubles her about the day the four-year-old vanished.

“We say ‘how, why’… we just can’t believe it,” Murray tells 7NEWS Spotlight.

“To be accused of doing something like this… you could not wish a more horrible experience on anyone.”

Josie Murray speaks with 7NEWS and Spotlight.Josie Murray speaks with 7NEWS and Spotlight. Credit: 7NEWS/Spotlight Gus Lamont disappeared in September last year. (HANDOUT/SA POLICE)Gus Lamont disappeared in September last year. (HANDOUT/SA POLICE) Credit: AAP

In the interview, Murray – who was interviewed by police but never charged – also reflects on the moment from the day Gus disappeared that continues to trouble her.

The investigation will uncover the potential clues police may have missed during the major crime probe into the missing boy, spanning nine months and 11 searches of the outback station.

“There appeared to be something there,” Murray says.

Police have searched the outback station multiple times.Police have searched the outback station multiple times. Credit: 7NEWS Footage of little Gus Lamont.Footage of little Gus Lamont. Credit: 7NEWS

7NEWS Adelaide crime reporter Hannah Foord joins Michael Usher to piece together the timeline and the unanswered questions in one of Australia’s most perplexing missing persons cases.

“This is the interview that could provide answers to the many questions being asked about the disappearance of little Gus,” Usher said.

“His grandmother has never spoken before, but in an extraordinary set of circumstances has now given her first interview.”

You can watch the story first on 7NEWS Adelaide this Sunday at 6pm, followed by the full interview on Spotlight at 8.40pm on Seven and 7plus.

SOURCE: https://7news.com.au/news/crime/grandmother-of-missing-toddler-gus-lamont-breaks-silence-in-major-7news-spotlight-exclusive-c-22447603