It had been nine years since Mr Atkins was last seen leaving Sydney nightclub ARQ with his boyfriend, 20-year-old Matthew Leveson, on September 23, 2007.

Mr Atkins had long rejected any involvement in his boyfriend's suspected death and had been acquitted of his murder and manslaughter in 2009.

But in the early hours of Thursday, and after persistent questioning at an inquest last week, he relented.

It is understood the 53-year-old provided information to police as to where Mr Leveson's body might lie in the Royal National Park south of Sydney.

He could point out the leafy area, off a bend in the road not far from a train station, but couldn't remember the exact grave site.

It was a tremendous step forward in an unsolved case that had caused deep anguish to Mr Leveson's family.

His parents Mark and Faye Leveson had hoped the recent inquest into their son's disappearance would help them finally find his body.

Over the years they had driven through the national park, picking random sites to start digging for their son's remains.

There is a "strong possibility", police say, they will now get that result.

In a rare but potentially successful move, Mr Atkins was ordered in the Coroner's Court to give evidence under immunity, meaning it could not be used against him in any future criminal proceeding.

Police dogs and forensic teams will return to the search site over the coming days with the aim of finding Mr Leveson's remains.

The inquest was adjourned on Thursday with Mark and Faye Leveson leaving arm-in-arm.

"I'm sorry but for the time being we just can't talk," Mr Leveson said outside the Coroner's Court in Glebe.

"The police have asked us not to say anything at this stage, so we've got to respect that.

"Please understand when we can talk, we will but not right now.

"Thank you so much for your interest."

Mr Atkins had lost a legal battle earlier this year in the NSW Supreme Court to avoid giving evidence following a ground-breaking ruling by Deputy Coroner Elaine Truscott.

Last week he faced days of relentless questioning about the final moments of his boyfriend's life and his questionable actions afterwards.

At one point, Mr Atkins suggested Mr Leveson could have still been alive and travelled overseas to start a new life.

"You know Matt is dead don't you?" counsel assisting, Lester Fernandez, put to Mr Atkins.

"No," Mr Atkins responded.

"Could Matt be alive?" Mr Fernandez continued.

"He could be," Mr Atkins said.

Mr Atkins was also quizzed on why he bought a mattock and tape from Bunnings the day after Mr Leveson was last seen.

Mr Atkins suggested he was an aspiring green thumb, despite not having a garden.

During one dramatic and unusual point in his evidence, he was handed a mattock and asked to demonstrate what he was do with it.

He was also handed tape and tomato plants and was asked to demonstrate how he planned to connect his own seedlings to stakes, as he claimed was his intention for the tape.

"What else are mattocks used for?" Mr Fernandez asked.

"That's all I thought ... digging up gardens," Mr Atkins responded.

"Digging a grave would you agree?" Mr Fernandez continued.

"Could be."

"Somewhere like the national park down south where you live, agreed?" Mr Fernandez said.

"Could be anywhere."