Gus Lamont updates LIVE: Police detail bombshell development in case of missing four-year-old boy

South Australian Police are expected to make a significant announcement today in the search for missing toddler Gus Lamont.

The officer in charge of the state's Major Crime division, Detective Superintendent Darren Fielke, will hold a press conference at 1pm local time (1.30pm AEDT).

Unearthed documents and local sources have revealed that the family of missing South Australian boy Gus Lamont has a complicated - and tragic - history.

Daily Mail revealed in October that the four-year-old's grandmother, trans woman Josie Murray, had not given up hope of finding Gus, who vanished from the front yard of his family's homestead at about 5pm on September 27.

Now, we can reveal more details about Josie's past on the remote Oak Park outback property, located 40km south of Yunta.

Pictured is Gus' grandmother, trans woman Josie Murray

Gus' mother Jessica is pictured as an infant, sitting on mother Shannon's lap

According to business records dating back to 1999, Josie's life partner Shannon Murray - a woman - used to work the sprawling sheep station with her father, late war hero Vincent Pfeiffer.

Shannon - known as Shan - was registered as a joint entity of Oak Park Proprietors alongside Vincent, who was nicknamed Vin.

It is believed that Vincent's wife - Shannon's mother - Clair Jones had previously inherited the station from her side of the family.

A Robert Murray also appeared on the public document, though this name vanished from records in 2015 - replaced by the name Josie Murray.

It is not suggested that any members of Gus' family are involved in his disappearance.

Gus Lamont was last seen at his grandparents' homestead at Oak Park Station, a 60,000ha property 40km south of Yunta, on September 27.

The four-year-old was in the care of his grandmother, Shannon Murray, while his mother Jessica and grandparent Josie were tending sheep about 10km away.

Police said Shannon was the last person to see Gus, at about 5pm, when he was playing in the sand outside the homestead.

When she went to call him inside about 30 minutes later, he had vanished without a trace and the family reported him as missing three hours later.

At the time Gus went missing, his father, Joshua Lamont, was living about two hours away from Oak Park and was not present when his son disappeared.

Although hundreds of police officers, dozens of soldiers, a small army of volunteers and an Aboriginal tracker have scoured tens of thousands of acres of Outback, the blond, curly haired little boy has not been found.

The only trace of Gus was a single footprint found about 500 metres from the homestead - which police have since cast doubt on.

There is little hope he will be found alive.

At the time of his disappearance South Australian Assistant Police Commissioner Ian Parrott said they believe that Gus wandered off and was not taken, as the only people who travel on the nearby road are station owners.

'Everything that we have found to date, every piece of information and evidence that we have explored to date, indicates that, as best as we know, Gus has wandered off from this property and we have not been able to locate him.'

Locals believe the four-year-old may have fallen into a disused and unmarked mine.

The area is dotted with mines and wells from more than a century ago.