Gus Lamont’s grandmother is set to break her silence in her first sit-down interview ever, as the four-year-old remains missing eight months on. 

Josie Murray will open up about the devastating impact of the little boy's disappearance in a Channel Seven Spotlight interview on Sunday night.

Josie was visibly emotional as she spoke to camera: 'How? Why? We just can't believe it.'

The exclusive sit-down promises to shed light on the 'clues police missed' despite extensive searches for the child.

Spotlight presenter Michael Usher said the segment 'could provide answers to the many questions being asked about the disappearance'.

'Even the South Australia police still want answers,' he said.

'Gus's grandmother has never spoken before, but in an extraordinary set of circumstances has now given her first interview.'

Detectives have been told Gus was last seen playing in a sandpile outside the remote homestead owned by Josie and Shannon Murray on September 27 last year 

Gus was said to be at home with grandmother Shannon and baby brother Ronnie, while his mother Jessica and grandmother Josie tended sheep elsewhere on the property.

However, in February, police alleged key timelines on the day Gus vanished 'did not match up' and declared his disappearance a major crime investigation.

Detectives also revealed that one of Gus's grandparents had become a suspect and stopped cooperating with police - a claim both grandparents deny. 

Police have refused to elaborate or confirm which grandmother is now their suspect, leaving the events of the day Gus vanished shrouded in mystery.

In the first weeks of the hunt for him, a friend of Gus's father Joshua told the Daily Mail the musician did not get along with Josie and was unhappy about his children living on the farm.

Daily Mail also revealed Joshua had been renovating a home about two hours away in Belalie North for his young family, with plans to move there before Gus started school.

For years, Joshua was a regular at Oak Park Station, helping around the property and even filming music videos for his band in the paddocks.

It is understood he and Jessica had separate accommodation on the station and lived there on and off after Gus was born.

Exactly when and why the family relationships soured has not been made public. 

In January, police executed search warrants at the remote property, seizing several items, including vehicles and electronic devices, for forensic examination.

After those fresh searches, police publicly ruled out both of Gus's parents as suspects, while revealing the unidentified grandparent was now a person of interest.

It is understood Jessica moved out of Oak Park Station around the same time, relocating to Adelaide with Joshua and their youngest son, Ronnie. 

On Friday, Josie faced Adelaide Magistrates Court, for sentencing after pleading guilty to acquiring, owning or possessing a sound moderator, a device more commonly known as a silencer or suppressor.

She was charged in February - in the midst of the hunt for the missing youngster - and she entered her plea in writing ahead of Friday's sentencing hearing.

The device, which is designed to reduce the noise of gunshots, was found on the property on January 15 during the massive police search for the child.

Josie appeared in person for the hearing, supported by close friend Bill Harbison, who spoke to the media on behalf of the family when Gus first disappeared. 

The court was told Josie had owned the silencer legally for several years but did not inform authorities she had it when the law changed in 2017, requiring permission.

Josie's lawyer Andy Ey said it had been a 'very difficult time' for his client.

'To address the elephant in the room, this has been an extremely difficult time for her family - her grandson went missing last year,' he said. 

'This is a serious matter, but it is not some James Bond movie where a villain or assassin is walking around corners taking out targets with barely the whisper of a gun.'

Police have confirmed they will return to the property in the coming weeks.