The Australian man would wear a brown coat, no matter the season, and pace up and down a Sydney street.

He rarely spoke, his neighbours said, but when prompted would sometimes mumble "hello".

He secluded himself in his home in Greenwich, a suburb of Sydney's Lower North Shore, living in squalor behind barricaded windows and locked doors.

Neighbours told 9 News Australia that the man, identified as Bruce Roberts, was discovered dead last year at his home. Outside, old tires were still piled up with wood and pieces of cardboard, according to the Australian Broadcasting Corporation. Inside, it was much worse.

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While clearing rubbish from the house this week, crews uncovered a mummified body either under a rug or rolled up in one in the back of the house, according to neighbours and police.

Though it's unclear how long the body had been decomposing in the home, police said in a statement that it had been there for "a considerable time". It's also unclear whether the quiet man who lived there had anything to do with the person's death.

Authorities responded to the scene on Tuesday and opened an investigation to determine who the person was and how he or she died.

SUPPLIED Squalor inside a hoarder's house. Not the home in this story. (File photo)

"The occupant of the home died close to a year ago and the owners organised for the property to be cleaned this week," police said. The authorities added that the recently discovered death is being "treated as suspicious".

Neighbours described Roberts, the man who lived there, as a "recluse" and a "hoarder", according to the ABC.

Authorities have not confirmed the man's name.

One neighbour said he came across as "childlike."

"He was [in his] late 50s or 60s, had the same brown jacket on, he was childlike in a way, he just had no expressions, nothing," the neighbour, who was not named, told the ABC.

"You'd say hello and he'd just mutter 'hello' or just not notice. He lived in this tiny little house on the corner, it's completely overgrown and you can see rubbish in the garden."

Robert and Gayle Meagher, who said that they lived next door to the man for decades, told the news organisation that his parents owned the home and that he had lived there for 40 or 50 years.

"When he died, I was really upset and I was worried that we were next door and what could we have done, but the home was not a very healthy environment, so there was nothing we could have done," Gayle Meagher said.

She told 9 News that she was saddened this week when crews discovered a second body inside the rubbish-filled home.

"The workmen who had been clearing the home said that they had found a body under a rug in the backroom," she said, adding that she and her husband were "shaken" by the news. "It was very creepy."

"It's very sad, especially when you don't know how it happened," she said.

In a similar case this year in Wales, authorities were excavating a hoarder's home and discovered a woman who lived there buried under piles of papers, and rushed her to a nearby hospital. The woman's mother, who had also lived there, was later found dead.

In Sydney, police said they are awaiting results from a postmortem examination to help determine the circumstances of death of the newly found remains.