A sad theory has emerged in the case of the home intruder killed by a Sydney dad.

Police are looking into whether an intruder who died at the hands of a homeowner after breaking into his Sydney property, was in there accidentally.

Brad Soper, 35 was found barefoot and hiding behind a couch in the Schwartz family home in the early hours of Sunday morning.

Johan Schwartz was only alerted to his presence by his barking dogs and went to investigate while his wife and young baby slept in the next room.

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Fearing for their safety upon finding Mr Soper an altercation broke out, and it’s understood Mr Schwartz got the intruder in a headlock, where he fell unconscious.

Despite desperate calls to triple zero and seven minutes of CPR, Mr Soper couldn’t be revived.

Police initially thought the body builder and gym owner forced entry into the property in Sydney’s south west, but the investigation is now looking into whether he was disorientated and high on drugs.

His friends admit he was struggling with a cocaine and steroid addition.

His father has told the Daily Mail his son was still “suffering from a broken heart” at the time of the break in.

Raymond Soper said his son's mental health had deteriorated last year after he split from his long-term partner.

He also said he didn't know why his son would've broken into the property, only to say it was "Out of character. We feel like he's had some kind of break-down or something."

"There's no way he'd go into anyone's place intentionally, there's just no way."

A friend told the Daily Telegraph; "He had some personal issues, like everyone else, there was nothing in his personality that would ever indicate anything like this."

Neighbours reported seeing him wandering around the neighbourhood in a "zombie like state" before slipping in through the Schwartz' open garage.

Mr Schwartz, who is said to be devastated, has spent the past week at home with his family after being interrogated for 10 hours by police on the night of the incident.

It's understood homicide detectives have advised NSW detectives not to charge Mr Schwartz - in NSW a person is allowed to defend themselves if someone invades their property with the use of "reasonable force."

An autopsy was performed on Mr Soper's body yesterday, but it could be weeks before the results are in - which will prove if Mr Schwartz used any type of "excessive" force to restrain him.