Missing four-year-old Gus Lamont’s grandmothers have released a statement through their lawyers, claiming they are “devastated” police have declared his disappearance a major crime.

Gus went missing from his family’s 60,000 hectare sheep station in September last year, and was initially thought to have wandered off.

He was last seen playing outside the homestead, which is about 300km inland from Adelaide.

An enormous search operation was launched, with ground crew covering almost 100 sq km and aerial searches covering more than 700 sq km.

After about a week, that rescue mission sadly became a recovery mission as hopes of finding Gus (August) alive waned.

During the search, police consistently said that the family was cooperating, that there was no evidence of foul play, but that they could not rule anything out.

Four months later, and police believe someone in his family was involved.

South Australia police (SAPOL) declared his disappearance a major crime on Thursday, and said that the suspect was someone who lived at the station.

Lawyers have confirmed they are acting for his two grandmothers.

Andrew Ey, of Mangan Ey and Associates, is acting for one grandmother, Josie Murray. Casey Isaacs, of Caldicott + Isaacs Lawyers, is acting for the other, Shannon Murray.

_{Sign up: AU Breaking News email}

On Friday, the lawyers released a joint statement saying that their clients would not be doing any interviews or making any comments, except for the following:

“We are absolutely devastated by the media release of SAPOL Major Crime. The family has cooperated fully with the investigation and want nothing more than to find Gus and reunite him with his mum and dad.”

On Thursday, Det Supt Darren Fielke, the officer in charge of major crime, said that after the extensive search, they now thought Gus had not wandered off, nor had he been abducted.

Police had “identified a number of inconsistencies and discrepancies” in the information they received from family members, he said.

“As a result of these inconsistencies, and investigations into them, a person who resides at Oak Park station has withdrawn their support for the police and is no longer cooperating with us.

“The person who has withdrawn their cooperation is now considered a suspect in the disappearance of Gus.”

Police seized a vehicle, a motorbike and electronic devices in mid January.

When four-year-old Gus first went missing, a frantic search began immediately.

“Four-year-old Gus Lamont wandered off from the Oak Park Station homestead, approximately 43km south of the Yunta township on Saturday, 27 September,” assistant commissioner Ian Parrott said on 3 October.

“Gus was seen outside at 5pm on Saturday playing on a mound of dirt by his grandmother. At 5.30pm she has gone outside to call him in, only to find him missing.

“According to a family member, he is a shy but adventurous child. While a good walker, he has never left the family property previously.”

He disappeared from the homestead wearing a grey sun hat, a blue Minion T-shirt, light grey long pants, and boots.

Not long after he was last seen, police started searching the area with the help of a helicopter and infra-red camera. The next morning, a drone was brought in, then divers, to search dams and tanks.

Within days, trail bikes, all-terrain vehicles, dogs, a tactical unit, Australian defence force personnel, mounted police, police cadets, emergency services, community and family volunteers, and an Aboriginal tracker joined the search.

On 30 September, Gus’s family released a statement thanking those in the search, asking for privacy and describing their heartbreak.

“We are devastated by the disappearance of our beloved Gus on Saturday afternoon. This has come as a shock to our family and friends, and we are struggling to comprehend what has happened.

“Gus’s absence is felt in all of us, and we miss him more than words can express. Our hearts are aching, and we are holding on to hope that he will be found and returned to us safely.”

On 3 October, police prepared the family for the fact Gus might not have survived.

“While those involved in the search have been hoping for a miracle, over the past 48 hours, the search has shifted to a recovery operation,” Parrott said.

They had found no sign of Gus, except for a single small footprint that yielded no further information.

Fielke said police are still determined to find Gus and return him to his parents.

Anyone with information should contact Crime Stoppers on 1800 333 000.