South Australia’s top cop says two relatives of missing four-year-old Gus Lamont are no longer cooperating with investigators, as the desperate search for the child stretches into its fifth month.

Grant Stevens told ABC Radio Adelaide on Wednesday that while detectives remain in close contact with Gus’s parents, “other members of the family” have withdrawn their support.

“As far as I’m aware, it’s status quo,” he said. “We are still working with Gus’s mum and dad and there are other members of the family who are no longer cooperating.”

A South Australia Police spokesperson confirmed to that “two family members are now only communicating via their legal representatives”.

Police first declared the case a major crime on February 5, revealing that a person who resides at Oak Park Station had stopped assisting investigators and was now considered a suspect. Officers have repeatedly stressed the suspect is not Gus’s parents, Josh or Jess Lamont.

Gus’s grandparents, Josie and Shannon Murray, had earlier issued a statement saying the family had “cooperated fully with the investigation”. Police have not identified the two relatives who have since ceased cooperation.

Nearly five months after their son vanished, Josh and Jess Lamont released an emotional public appeal on February 24, describing themselves as “united in grief” and begging anyone with information to come forward.

“We are united in our search for answers about what happened to our little boy, Gus, who means everything to us,” they said. “Our lives have been shattered, and every moment without him is unbearable.

“If someone knows what happened, we are pleading with that person – or anyone who may have seen or heard anything – to please come forward. Even the smallest detail could give us the answers we so desperately need.”

The couple also released new video and another photograph of Gus in the hope it might jog someone’s memory, thanking police, emergency services, ADF personnel, volunteers, Indigenous trackers and supporters who have scoured the vast outback around Oak Park Station.

“All we want is to bring Gus home and understand what happened to our beautiful boy,” they said.

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

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

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

Detectives from Task Force Horizon continue to pursue new leads, with police reiterating that “nothing is off the table”.

Images: SA Police