Crime experts say police have deployed a ‘masterful tactic’ in the Gus Lamont investigation as detectives announce there is a single suspect in the boy’s disappearance.

Ex-detective turned private investigator Charlie Bezzina told the Daily Mail that police declaring Gus deceased, and reclassifying the investigation as a major crime rather than a missing child case, speaks volumes about what may be unfolding behind the scenes.

Police publicly revealed on Thursday that a family member ‘who resides at Oak Park Station’ – not one of Gus’ parents – had withdrawn co-operation in the investigation, and that person is now a suspect.

Police also confirmed they believe the four-year-old is dead.

Mr Bezzina said the shift from someone cooperating with police to being described as ‘no longer cooperating with us’ often happens when investigators formally caution a person as a potential suspect.

‘If you have to caution someone when they are talking to police, that will shut them up,’ Mr Bezzina said.

‘Then it’s a matter of them saying, “I don’t want you talking to me without my lawyer present,” or the lawyer saying, “If you want to talk to my client, it will only be when I am present.”‘

After the announcement, it was revealed that two members of Gus’s family had hired separate lawyers.

There was a major development in the investigation into Gus Lamont, four, this week as police revealed they had found no evidence he had been abducted or walked off

Police declared that neither of Gus Lamont’s parents, Jessica and Josh (pictured) were suspects in the ‘major crime’ case that was their son’s disappearance

Little Gus vanished from a remote property, Oak Park Station, sparking a massive South Australia Police investigation

Gus’s grandmother Josie Murray, a transgender woman, hired Adelaide criminal lawyer Andrew Ey, while his grandmother Shannon Murray sought the legal services of Casey Isaacs, also from Adelaide.

Mr Bezzina said it could create a conflict of interest for Gus’s two grandparents to share the same legal representation and that the police announcement resembled ‘a form of pressure.

‘By publicly exonerating (Gus’s) parents that may be putting pressure on too.’

‘While the uniformed police are doing line searches looking for the missing person, simultaneously criminal investigators are doing their work,’ he said.

He explained that police record detailed statements from everyone present early in the investigation so those accounts can later be checked against forensic evidence. If those stories later don’t match the evidence, investigators focus on why.

Mr Bezzina said detectives may then try to persuade people with knowledge of the case to come forward.

‘I know in my investigations I can pull the emotional heartstrings of a person or throw them a life buoy “if you have had anything to do with it, or know anything and can help …”, that sort of thing.’

Missing Gus’s grandparents Shannon Murray (left) and Josie Murray (right) have engaged separate lawyers after SA police announced they had a main ‘suspect’ and the case was now a ‘major crime’ investigation

Detective turned private investigator Charlie Bezzina (above) said forensic examination of a motorbike seized three weeks ago could yield evidence

A massive air and ground search by police, Army and the SES of Oak Park failed to turn up any trace of the boy

Ex-cop turned lawyer Michael Kuzilny

Police revealed they searched Josie and Shannon’s remote property on January 14 and 15 and said items seized during the search included a vehicle, a motorcycle and electronic devices.

Mr Bezzina said police would be forensically examining a motorbike on the property in the hope of finding hair, blood or tissue belonging to Gus – ‘one little piece of evidence’.

‘Of course accidents happen on farms and even if that points them to what they believe happened, the police have to prove it before they charge someone or go to court.’

Long-time lawyer Michael Kuzilny told the Daily Mail detectives that examining the computers and phones removed at the same time from the property where Gus disappeared could have uncovered hard evidence of differing accounts of what actually happened.

He said an arrest could be just days away and the investigation might have already been enhanced by listening devices, telephone taps and covert surveillance.

Gus vanished around 5pm on September 27 last year from remote Oak Park Station – a 60,000ha South Australian property about 40km south of Yunta.

The original account of the disappearance was that the boy had been playing in sand in the vicinity of the homestead with Shannon, while his mother Jessica and Josie were tending to sheep about 10km away.