Son killed NSW family to 'protect them'

When Carlos Lopez killed three of his family members in their western Sydney home, he thought he was saving them, a court has heard.

Lopez was charged with the stabbing murders of his 61-year-old mother Olga Novosadek, his stepfather Pablo Novosadek and his brother Paul Novosadek at St Johns Park in July 2012.

The 44-year-old also killed the family's two pet chihuahuas.

At a judge alone trial on Monday, the Supreme Court heard Lopez was pleading not guilty to the murders on the grounds of mental illness.

Crown expert and forensic psychiatrist David Greenberg told the court that Lopez had paranoid schizophrenic disorder and that at the time of the stabbings believed extra-terrestrial demons were using his family members as hosts.

"He felt he was morally justified in acting that way because the demons were descending ... and in order to protect them and save them he had to kill them," Professor Greenberg said.

Facts tendered to court reveal that on the morning of the stabbings, Lopez called Triple 0, saying "I killed my family".

When police arrived at the home and asked him his name, Lopez said: "Satan".

In subsequent interviews with police, Lopez told officers: "I became aware, he, Satan, was jumping between the bodies. Between Mum, Dad, Raul and the dogs. I thought if he didn't have a body, he didn't have a host.

In the days leading up to the killings, the agreed statement of facts say Lopez, who worked as a fork lift driver, had told one of his colleagues that his name was "Zioba" and that he was a "Zionite".

"My physical name is Carlos, I'm only here for a short time," he allegedly said.

Justice Peter Garling will hand down his decision on Friday.