The father of teen jihadist Jake Bilardi has revealed his son was an aggressive and psychologically disturbed child.

John Bilardi told 60 Minutes Jake had threatened him and his former wife with weapons as a young boy and harmed himself.

One incident stood out clearly.

"My wife at that time was calling out to me, screaming," he said in an interview aired on Sunday night.

"I run out into the room where she was and she was backed up into a corner with Jake … thrusting a pair of scissors at her."

Mr Bilardi said his son then turned on him before he was able to prise the scissors from his hands and hold him in a bear hug.

"The strength that he had as a young kid of six years old was incredible," he said.

A home video shown on the program depicted Jake as a young boy unable to engage with his brothers and sisters as they played a game.

Mr Bilardi said he blamed himself for not being able to help Jake, who allegedly blew himself up in a suicide attack in Iraq earlier this month.

"I knew there was something not right with his behaviour, " he said.

"He had psychological problems or mental issues that should have been addressed and I feel totally responsible.

"I should have been there for him and he obviously needed help and, as a parent, I wasn't able to do that.

"One of the main reasons why I'm doing this is that I would just like everyone to know that the buck stops here with me. He was my son."

However, Mr Bilardi also described his son as a softly spoken, shy, intelligent young man who "could have had a bright career".

"That's the memory. The rest of it, as far as I'm concerned, can go to hell," he said.

Mr Bilardi was a stay-at-home dad until he and Jake's mum divorced.

He said Jake had loved soccer, video games and The Simpsons.

But a bitter split meant Mr Bilardi lost contact with Jake and his five older siblings, who all grew up in Craigieburn, until their mother died of cancer three years ago.

It was then that Mr Bilardi learnt of his son's conversion to Islam.

"Just out of the blue he said, 'I've gone Muslim', and of course that, I literally went, sort of fell back in me seat," Mr Bilardi said.

"And being atheist myself and his mother was pure atheist, that shocked me to hear that."

Mr Bilardi said Jake had become a loner who spent all his time in his room living a second life online, obsessed with radical Islam.

He accused the Islamic State recruiters of murdering his son, who was a "soft target".

"He was a trophy that they paraded online. They gloated about how they had recruited this boy who didn't even have a Muslim background," he said.

"They used him. They are murdering people, and including my son. They murdered him."

Mr Bilardi said he was shocked to see his son in online photos with extremists last December.

"Just to see him sitting there with that gun is just unbelievable," he said.

"I just couldn't believe that was my son."

When asked about allegations that Jake had stockpiled bombs with the intent of blowing up Australians, Mr Bilardi said that was not the son he knew.

"He was just a shy, lonely young man," he said.

He issued a warning to Australians.

"It's going on, it's happening, it's real," he said.

Jake's friends told 60 minutes he was "obsessed" with issues in the Middle East.

"He said he would sacrifice his life for Islam," said one.

They said he turned to Islamic State recruiters after being repeatedly bullied at school.