Police say a suspect has been identified over the disappearance of a four-year-old boy who went missing in the South Australian outback.

Gus Lamont was last seen playing outside his home on a remote sheep station near Yunta, about 300km (186 miles) from Adelaide, on 27 September.

His grandmother left him alone for about half an hour before checking on him, only to find the boy missing, prompting one of the largest land and air searches in the state's history.

Police said a person who lives on the property has been identified as a suspect but confirmed the boy's parents were not under investigation.

In the days and weeks after Gus was reported missing, police conducted extensive searches, covering about 470 sq km - an area roughly twice the size of Edinburgh.

Police wound down efforts and appointed a 12-member taskforce to continue the investigation, which sifted through previous statements given by family members that revealed inconsistencies concerning the timeline around Gus's disappearance.

Detective Superintendent Darren Fielke stated, 'As a result of these inconsistencies, a person who resides at Oak Park station has withdrawn their support for the police and is no longer cooperating with us.'

Investigators initially considered three possible scenarios regarding the boy's disappearance—he could have walked off, been abducted, or a person known to him may be involved. Given the remote location of the property, abduction was ruled out, and there was no evidence indicating Gus had merely wandered off.

Fielke reiterated, 'We'll continue to thoroughly and meticulously investigate the disappearance of Gus until we get an outcome.' The investigation remains a top priority for law enforcement as they strive to bring Gus back home.