Shane Snellman's fully clothed body was uncovered by cleaners removing hoarded material from Bruce Roberts' Greenwich home on May 29, 2018.

The body was in an advanced state of decomposition, coroner Derek Lee said on Thursday.

A later autopsy found the remains were "completely mummified".

Mr Snellman, who was 39, had likely died in October 2002 from a gunshot wound on the left side of his neck after breaking into the home and being confronted by Mr Roberts, Mr Lee found.

Mr Roberts, described by neighbours and family as socially awkward, unpredictable and reclusive, never alerted police to the body.

Instead, he continued with his habit of piling boxes in the spare room and other parts of his house until his death at the age of 60 in mid-2017.

But the placement of more than 70 air fresheners around the body was "a conscious effort to mask the smell of his decomposing remains", Mr Lee was told.

By the time police were called in late July 2017, Mr Roberts had not been seen for eight weeks and a neighbour had noticed an unusually large build-up of uncollected mail in his letterbox.

After gaining entry with the help of firefighters, officers found the hoarder's body slumped in a hallway over a bar heater.

The heater was still operating and Mr Roberts' heard, face, right shoulder and chest were noted to be burnt.

But Mr Snellman's body remained undisturbed even after police returned to the home in mid-May 2018 when a relative of Mr Roberts found a firearm and ammunition.

"He was an extreme hoarder," Leading Senior Constable Shane Spencer told the Coroners Court on Thursday.

"As we walked into the front door of the address, there were immediately items stacked from floor to ceiling.

"It was evident he never threw anything at all out."

A small path wide enough for a person to walk through existed between Mr Roberts' bedroom, the bathroom, kitchen and through the hallway to the front door, the officer said.

But two other bedrooms, including the one containing Mr Snellman's mummified remains, were "just stacked floor to ceiling with rubbish".

The inquest heard Mr Roberts had lived in the house on Greendale Street for at least three decades, becoming the registered owner after his mother's death in 1989.

He also inherited $1 million in shares, freeing him of the need to ever work.

More than $600,000 was in his account when he died.

In contrast, Mr Snellman endured a transient life - growing up in a boys' home, struggling with drug abuse and being jailed on multiple occasions for dishonesty and property offences.

He spent 10 months in jail aged 15 before being acquitted of a homeless man's murder. His last jailing, a one-year term for drug supply, ended in June 2002.

Three days before his last sighting on October 18, he withdrew $1, leaving 66 cents in his account.

"The contrast between the lifestyles of Mr Roberts and Mr Snellman, and the different locations that they were known to frequent, strongly suggests that there was no opportunity for them to meet prior to Mr Snellman's death," Mr Lee said.

"Further, given Mr Roberts' reclusive lifestyle and preference for little to no social interaction, it is most unlikely that Mr Roberts would have willingly invited Mr Snellman into his home."

The fatal weapon was likely one of the 13 guns, found along with a wealth of ammunition at the home.

The finding that Mr Snellman had broken into the Greenwich home devastated his estranged sister Belinda, who yelled "how dare you" at the coroner and said her brother knew Mr Roberts.

The coroner ruled Mr Roberts died of natural causes after an apparent collapse.

But he couldn't make a more precise ruling due to "thermal injuries" sustained either partly or entirely after death.

Australian Associated Press