Matthew Leveson's mum has written a heart-wrenching letter to the man who killed her son.

The mother of murdered NSW man Matthew Leveson has made a passionate plea to her son’s former lover to man up “and show us exactly where you buried my beautiful son” as a renewed search continues into a second week.

Diggers were back at work in dense bushland at the Royal National Park, south of Sydney, on Monday after a five-day search last week failed to uncover any trace of the 20-year-old’s body.

His parents – Mark and Faye Leveson – who’ve never given up hope of finding their son’s body after he went missing in 2007 – were back at the site first thing in the morning.

It’s expected they’ll be there again on Tuesday morning when the search resumes.

NSW Forensic Services officers were called on Monday when material of interest was uncovered.

But after an examination, it was determined to be from an echidna, a detective told an AAP photographer at the Royal National Park.

A NSW Police spokesman later confirmed there was no result on Monday and crews would return on Tuesday, weather permitting.

The search is the third in the past six months after police combed the site in November and January but failed to find any trace of Matthew.

Investigators were originally led to the remote roadside site by his former boyfriend, Michael Atkins, who was acquitted of the younger man’s murder in 2009.

Mr Atkins took detectives to the potential burial site after he was offered immunity from prosecution for perjury and contempt of court after admitting to lying at an inquest into the suspected murder.

An ongoing 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.

Faye Leveson wrote a long message on Facebook on Sunday.

“Michael Atkins, we have spent the last week watching on as the police dug for the 3rd time looking for Matt,” she posted.

“Tell us the truth, man up and come down and show us exactly where you buried my beautiful son. For once in your life DO THE RIGHT THING. You said you loved Matt. Love is not disposing of your loved one in the bush like a piece of rubbish.”

Ms Leveson ended her long post by stating: “I will search for Matty till the day I die. I promised Matty I will find him and I have every intention of keeping that promise.”