South Australian police have declared the disappearance of four-year-old Gus Lamont from a remote sheep station a "major crime", and say a suspect has been identified.
The child was reported missing from a family outback homestead about 43km south of Yunta on 27 September.
On Thursday, detective superintendent Darren Fielke, the officer in charge of the Major Crime Investigation Branch, declared the disappearance a "major crime".
"The search for Gus was based on him walking off from Oak Park Station and becoming lost. This is one of three investigation options that have been explored by the members attached to Task Force Horizon," he said.
"The other two investigation options are focused on Gus being abducted from Oak Park Station or whether someone known to him was involved in his disappearance and suspected death."
Investigators have found no evidence to suggest the child was abducted, Fielke said.
Search warrant executed at Oak Park Station
Police executed a search warrant at Oak Park Station on 14 and 15 January, Fielke said.
Detectives seized a number of items, including a vehicle, a motorcycle and electronic devices for forensic examination.
A person who resides at the sheep station has withdrawn cooperation with the case and is considered a suspect, Fielke said.
Gus' parents are not suspects in his disappearance, he said.
He said the search for Gus had been "unprecedented" and significant resources had been deployed.
Police said they conducted eight separate ground searches that extended to a radius of 5.47km from the homestead. The search area included three dams, which were drained. Police also searched six mine shafts within a 10km radius of the homestead.
Extensive aerial searches were also conducted.
Several locations around Oak Park Station were searched for Gus' remains on Monday, police said.
"Despite these extraordinary efforts, all of the combined searches have found no evidence, physical or otherwise, to suggest Gus has wandered off," Fielke said.
"I anticipate there will be further searches at Oak Park Station and at several sites on an adjacent national park to locate Gus as new information and intelligence comes to hand as the investigation continues," Fielke said.
"I can reassure the community that despite the complex and challenging nature of the investigation, Task Force Horizon will continue to thoroughly and meticulously investigate the disappearance of Gus until we get a resolution."
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