Investigators are looking into whether a body builder killed during a suspected home invasion in Sydney's south-west may have accidentally ended up in the Harrington Park property.

Key points: The police investigation is focusing on whether Bradley Soper was disorientated and high on drugs

The police investigation is focusing on whether Bradley Soper was disorientated and high on drugs Detectives travelled to Dubbo to interview Mr Soper's father about his son's mental health history

Detectives travelled to Dubbo to interview Mr Soper's father about his son's mental health history Homicide detectives advised against laying charges against homeowner Francois Schwartz

When his dogs started barking on Sunday morning, Francois Schwartz, 44, raced downstairs and found personal trainer Bradley Soper, 34, hiding behind his living room couch.

Fearing for his wife and young daughter's safety, the ABC understands Mr Schwartz challenged Mr Soper before he grabbed him in a headlock and called out to neighbours for help.

A source close to the investigation said Mr Schwartz's wife called police after Mr Soper lost consciousness, but he had already died by the time paramedics arrived at Westwood Court.

Police initially thought Mr Soper intended a forced entry into Mr Schwartz's home, but the investigation is now focusing on whether the Bringelly man was disoriented and high on drugs.

Mr Schwartz put Mr Soper in a headlock after finding him in his home on Sunday night. ( Supplied )

Detectives travelled to Dubbo in the state's central west to interview Mr Soper's father to determine whether his son had suffered from any long-term mental health issues.

Those close to Mr Soper claimed he was struggling to beat a cocaine habit, while others said steroid use eventually put the weight-lifting competitor in hospital for kidney failure.

After being interrogated for 10 hours, Mr Schwartz was released without charge from Narellan Police Station. He has spent the past few days at home with his family.

Friends of Mr Soper said a home invasion was "out of character" for him. ( Supplied )

In NSW, a person is allowed to defend oneself using "reasonable force" if someone invades their home.

Detectives from Camden Police are handling the investigation, but it is understood New South Wales homicide detectives have advised them not to lay charges against Mr Schwartz.

An autopsy was conducted on Mr Soper's body to determine the cause of death, but it could take weeks before the results are released.