South Australian police have confirmed they now have a suspect in the disappearance of four‑year‑old August ‘Gus’ Lamont, as the case is formally declared a major crime more than four months after the little boy vanished from a remote Yunta sheep station on September 27.

Detective Superintendent Darren Fielke said Major Crime investigators have been working through new information and have identified a person of interest.

Police said the person is not either of Gus’s parents.

“I am declaring the disappearance of Gus Lamont to be a major crime,” Fielke said.

“We have identified a number of inconsistencies and discrepancies in the information provided to us by family members.

“As a result, a person who resides at Oak Park Station has withdrawn their support for police and is no longer cooperating.

“That person is now considered a suspect in the disappearance of Gus.”

“A comprehensive forensic search was conducted of the Oak Park Station homestead, and a number of items were seized, including a vehicle, a motorcycle and electronic devices.”

Gus was last seen on September 27, playing outside the Oak Park homestead according to his family, while his grandmother cared for his younger brother inside.

Despite one of the state’s largest search operations — involving police, SES volunteers, Indigenous trackers, drones and helicopters — no significant trace of the child has been found.

The only physical clue remains a single footprint discovered about 500m from the property.

Fielke said the major crime declaration reflects the seriousness of the investigation and the extensive work underway behind the scenes as detectives continue to analyse evidence and pursue new leads.

However, they said police are confident Gus didn’t walk off into the outback.

“The ground searches and aerial searches have failed to locate Gus or any items belonging to him,” Fielke said.

“We have found no evidence, physical or otherwise, to suggest that Gus merely wandered off from the Oak Park homestead.

“We have a high level of confidence that he hasn’t wandered off.”

Police are also reviewing whether further targeted searches will be conducted around the vast outback region south of Yunta, where crews previously battled scorching heat, rugged hills and sparse vegetation during the initial 470sqkm search.

The property’s dams and outbuildings have been searched and tested, all during the eight separate searches for Gus Lamont

“Those dams have been searched twice. On one of those occasions, we drained the dams so police divers could satisfy themselves that Gus is not in any of them,” Fielke said.

“All outbuildings and the homestead have been searched multiple times, and some have been subjected to forensic testing.

“No stone is being left unturned.”

The tiny community of Yunta, home to fewer than 100 residents, has remained united in grief and uncertainty since the little boy disappeared. The confirmation of a suspect marks the most significant development in the case to date.

“We will continue to thoroughly and meticulously investigate the disappearance of Gus until we get an outcome,” Fielke said.

“We are all focused and determined to locate Gus and return him to his parents.

“Nothing is off the table.”

Police said further updates will be provided as the investigation progresses.