A man whose mummified body lay for more than a decade in the ramshackle Sydney home of a hoarder, had a led troubled life and was estranged from his family.

His body, believed to have been rotting inside the derelict Greenwich property for more than 10 years, has been named as Shane John Snellman.

READ MORE Mummified body rolled up in carpet in hoarder's home identified

He was known to police for numerous crimes, which AAP understands were low-level, and no missing persons report was lodged with authorities, NSW Police said on Tuesday.

His long-lost sister Tracy Trudgitt says the family lost contact with her older brother when he was placed in the welfare system.

She says she screamed and fell to the floor of her Sydney home when detectives told her they had found her brother's remains.

"I'm still in shock. I can't believe this has happened."

She told The Australian that Mr Snellman, who would have been 55 if alive, was one of five children.

She last saw her brother 10 years ago, during a jail visit, and says their father also tried to find him.

"He has never been forgotten," Mrs Trudgitt said on Wednesday.

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Mr Snellman at some point wound up dead in the run-down home of hoarder Bruce Roberts in the northern harbourside suburb of Greenwich.

A post-mortem examination showed he had suffered a number of injuries and his death is being treated as suspicious, investigators said last week.

A gun was recovered from the property during the search and is being tested by forensic experts, AAP understands.

A mobile phone, believed to be an older model Nokia, will also be examined for clues to Mr Snellman's fate.

Mr Roberts died of natural causes in the home in July 2017 and his body was discovered shortly after local shop attendants realised he had stopped going on grocery runs.

The piles of rubbish and junk which fill the home apparently meant Mr Roberts' body was removed without anyone noticing Mr Snellman's corpse in the living room.

AAP

The executor of Mr Robert's estate sent cleaners to the home last Tuesday where they discovered the remains under a pile of debris.

Mr Roberts was reportedly a familiar sight pacing about the leafy suburb.

While he would quietly exchange pleasantries with neighbours and passers-by, he has been described as a "loner" and "child-like" while police confirmed he had mental health issues.

It now seems investigators are being forced to consider whether Mr Roberts was living for years alongside Mr Snellman's corpse.