Matthew Leveson's family attack jury who acquitted their son's former boyfriend.

The father of murdered NSW man Matthew Leveson has told the man acquitted of the crime that he’s “no longer of any use to our family alive” after police found what could be the skeleton of his 20-year-old son.

After an emotional day at his son’s likely burial site in the Royal National Park south of Sydney, Mark Leveson on Thursday also slammed the jury which in 2009 acquitted Matthew’s boyfriend Michael Atkins of his murder two years earlier.

"If any of the jurors on Matthew's trial see this, what the hell were you thinking?" Mr Leveson told reporters.

"Look what you've done to us, this you could have solved many years ago yourselves. And lastly, Michael Atkins, to you, you are no longer of any use to our family alive."

Police found the human remains below a cabbage-tree palm at a site near McKell Avenue at Waterfall about 2.30pm on Wednesday which was to be the final day of their latest search. They've searched the national park on three occasions in the past six months after Mr Atkins led them to the site last year as part of a deal with the attorney-general for immunity from perjury and contempt of court.

The immunity applied to evidence Mr Atkins had been compelled to give at an ongoing coronial inquest where he denied killing his boyfriend.

Matthew's mother, Faye Leveson, also laid into Mr Atkins on Thursday when making an emotional plea for changes to the justice system and said her family had been "painted into a corner".

"They made us make a decision to bring our son home and for the killer to walk free - and we'd do it in a heartbeat to get him back, but our laws have got to change," Ms Leveson said.

"If that person had been convicted, he would have had an appeal on the conviction, he would have had an appeal against the sentence. The victims get nothing."

Police believe the skeleton belongs to Matthew but Detective Chief Inspector Gary Jubelin says they can't be completely certain yet.

"I can't say that with 100 per cent confidence until we get the forensic examinations carried out, but the circumstances in which we've found these remains lead us to believe they are Matthew Leveson's," he told reporters.

Listen: Meshel Laurie and Emily Webb discuss how a little girl from a loving family could grow up to become a murderer on Australian True Crime (post continues after audio...) 

Chief Insp Jubelin would not be drawn on what the discovery and potential new evidence could mean for Mr Atkins who was last reported to be working as an electrician in Brisbane.

"The matter's still before the coroner so it would be inappropriate for me to make any comment," he said.

"What I can say in relation to the scene here is that we will continue the examination tomorrow, possibly even into a third day."

The inquest into the death of Mr Leveson, who was last seen leaving Darlinghurst's ARQ nightclub with Mr Atkins in the early hours of September 23, 2007, is scheduled to resume in August. Legal experts say it's almost impossible Michael Atkins will face a fresh murder charge based on the fact human remains found in NSW bushland likely belong to his former lover Matthew Leveson.

Mr Atkins can only be charged on "fresh and compelling" evidence, but it's unlikely that will include the remains because of the deal he struck with the NSW coroner.

The bones were found in the Royal National Park south of Sydney on Wednesday, almost a decade after the 20-year-old was last seen with Mr Atkins at ARQ nightclub in Darlinghurst. Mr Atkins, who was acquitted of Mr Leveson's murder in 2009, was compelled to give evidence at an inquest last year.

‘What the hell were you thinking?’: Levesons lash out after discovery https://t.co/tIuhf7h9mg

— Illawarra Mercury (@illawarramerc) June 1, 2017

When forcing him to appear at the inquest, the NSW coroner gave Mr Atkins a certificate preventing any evidence obtained as a result of the hearing being used against him in criminal proceedings. Police started searching the national park in November 2016 after the attorney-general separately offered Mr Atkins - who admitted lying at the inquest - immunity from perjury and contempt of court if a body was found.

UTS law school Associate Professor Thalia Anthony says the fact the coroner gave Mr Atkins a certificate means the discovery of the remains likely can't be used as "fresh and compelling evidence" to overcome double jeopardy laws.

"It seems that his disclosure of the whereabouts of the body and anything associated with the body would not be able to be used against him to get through the double jeopardy threshold," Assoc Prof Anthony told AAP.

"On the basis of what he's told the coroner's court about the approximate location of the body, he can't be charged."

Former NSW Director of Public Prosecutions Nicholas Cowdery said whether a charge can be resurrected against Mr Atkins depends on what police find at the burial site.

"There's a slim possibility, I don't put it any higher than that," he told the ABC. "I think we need to be realistic."

He said even if DNA evidence was found at the scene, it could merely prove Mr Atkins and Mr Leveson had contact.

"It's the kind of contact that is important and whether or not it is establishes some kind of criminal connection of Atkins with Leveson."

We can keep our promise to Matt: Levesons https://t.co/kXyYaXwhEy pic.twitter.com/6N9l7EusuM

— Anna Lampugnani (@alampii) May 31, 2017

Mr Atkins has been living in Brisbane but sold his apartment at the beginning of this year after being banned from gay club The Beat amid a campaign to bar him from other venues across the country. His real estate agent says he did not provide a forwarding address and wished to remain anonymous. Trading websites list Mr Atkins as a licensed electrical mechanic in Queensland and NSW. He tried to fight the order compelling him to give evidence at the inquest in the NSW Supreme Court, but the action was dismissed.

Justice Lucy McCallum in her October 2016 judgment stated "the prospect that Mr Atkins will be retried is now very slim".

She said the coroner had considered the "family's all-consuming need simply to learn what happened" when granting the immunity certificate.

Assoc Prof Anthony said the certificate would also "presumably" protect him from civil proceedings.

"The whole purpose of providing that certificate is so that Mr Atkins would be completely honest," she said.

"I think trying to ... inflict some punishment through civil proceedings would violate that undertaking."

The deals were done after consultation with Leveson's family members.

NSW Attorney-General Mark Speakman has not commented on the prospect of a fresh prosecution, saying it would be premature before the remains are further analysed.