The grandparents of missing four-year-old Gus Lamont have released a joint statement through their lawyers after South Australian Police declared his disappearance a major crime.

The police released an update on Thursday after numerous searches failed to find any trace of Gus, who was last seen at the sprawling Oak Park sheep station in outback SA on September 27.

Detective Superintendent Darren Fielke said they now believed that Gus was dead, and could have been killed “deliberately or accidentally”.

He revealed that someone living at the remote property and known to Gus was being treated as a suspect.

Fielke confirmed two grandparents, Gus’s mother and younger brother were on the property when he disappeared, but stressed the person of interest was not the boy’s parents.

On Friday, Adelaide lawyers Andrew Ey and Casey Isaacs confirmed they were acting for Gus’s grandparents, Josie Murray and Shannon Murray, respectively.

The pair said their clients would not be participating in any interviews “nor commenting any further”, except to release a brief joint comment.

“We are absolutely devastated by the media release of SAPOL Major Crime,” the statement said.

“The family has co-operated fully with the investigation and want nothing more than to find Gus and reunite him with his mum and dad.”

It is common for witnesses to obtain legal advice and The New Daily is not suggesting any wrongdoing.

The remote farmhouse where Gus was last seen. Photos: SA Police

Gus’s disappearance sparked intensive searches spanning almost 500 square kilometres by hundreds of police and volunteers using aerial support and mounted units.

Fielke said on Thursday that the suspect had withdrawn co-operation in the investigation after “inconsistencies and discrepancies” were identified in the information they provided.

Investigators executed a warrant at the homestead on January 14 and 15, seizing items including a vehicle, a motorcycle and electronic devices.

“All of these items are now subject to forensic testing,” Fielke said.

The four-month investigation had “taken many twists and turns” and Gus’s parents were shocked, he said.

“It’s challenging, it’s delicate at times when you’re dealing with family members … our people have been unwavering and kept an open mind,” Fielke said.

–with InDaily