Augustus “Gus” Lamont was last seen playing in the sand at his family’s sheep station near the town of Yunta in South Australia on September 27 about 5pm.

When his grandmother went to call him inside about half an hour later, the preschooler was nowhere to be found.

An immediate 10-day search for the boy, which included helicopters, drones and Aboriginal trackers, failed to yield any clues.

Four-year-old Augustus “Gus” Lamont. Picture: Supplied

A footprint found in the original search. It was later ruled out by police. Picture: Supplied

However, on Monday, police and army members announced they would be returning to Oak Park Station to search an area outside of a zone already searched by authorities.

Mr Jubelin, the former lead detective in the William Tyrrell investigation, told news.com.au the fresh search suggested police were planning to look “further afield” for the “sake of completeness” as all signs now point to third-party involvement.

Given the rural terrain, Mr Jubelin said one line of inquiry would be whether Gus was taken by an animal.

“Police would be looking at, did young Gus disappear through misadventure, wander off, or was there some form of intervention, either human intervention or even, given the nature of the land out there, perhaps wildlife,” Mr Jubelin told news.com.au.

“Things can be missed, minute things can be missed.”