The child protection worker had come to the boy Bradyn Dillon's school following a child concern report of an injury to his ear.

But when his father Graham Dillon arrived the child protection worker feared for their life and called police.

Dillon reported to a case worker from a Canberra fathers crisis service that he couldn't go to the hospital with the boy to be assessed because he couldn't promise he wouldn't harm someone.

While Dillon reported that he wanted to take the child out of school, the worker did not think the man was trying to avoid detection of abuse.

He was unaware it was the fourth report made about the family in relation to facial injuries and believed there had just been the one.

Dillon also once reported to the support worker that he had bashed a man unconscious outside his home while the boy was inside.

But records suggest that information may not have been communicated to territory child protection authorities.

Dillon, 41, is serving more than three decades in jail for murdering the boy in horrific circumstances on February 15, 2016.

An inquest is examining the lead up to the nine-year-old's death and how he fell from the radar of authorities.

The support worker, whose name is suppressed, told the ACT Coroner's Court on Thursday Dillon had been referred to the service in 2013.

He reported being kicked out of his partner's home after an incident in which police were called and was sleeping rough with his son.

The support worker's role was to provide crisis accommodation for the man and his son and help him get a permanent home.

Dillon did not present as a domestic violence offender.

The support worker said it was awful to think of now, but he believed Dillon was an example of what all their clients should be.

His crisis accommodation was always in pristine condition and he was always cooking and making improvements.

"I genuinely thought he was an amazing dad," he said, "this was a huge shock when this happened, I just couldn't believe it at all."

But he agreed that he had been conned.

He said he'd been in the services for some 14 years and had a good track record.

He had spent hundreds of hours with Dillon and the boy, and regularly turned up to the home announced for spot checks.

"I thought didn't believe a person could keep up an act for so long. The amount of energy that would have taken is phenomenal.

"For the first sort of year after this I was in a pretty bad way. I just kept thinking something went wrong when he was out of our care."

He said Dillon was an adept service user.

He knew where to go for what and was always grateful.

Dillon told the service that Victorian authorities had removed the boy from his mother, with whom he had split years earlier, because she had neglected him and exposed him to domestic violence.

The support worker said the service usually sought to verify that kind of information, and in this case Dillon provided Centrelink statements showing he had one hundred per cent care of the boy.

The support worker said the boy was friendly and awesome, but there were times when Dillon was "flat" and would cry.

The worker said Dillon would tell the boy about how he was depressed and didn't want to live.

During these times Dillon would keep the boy home from school to help comfort him.

The support worker said he spoke to Dillon about the appropriateness of what he was saying to the boy, about making a plan that didn't involve the boy as his support, and about ensuring Bradyn went to school.

He said they also spoke about techniques to manage his anger.

Dillon showed the service a domestic violence order he had against the boy's mother, and told the worker she had tried to kidnap the boy and had sent third parties in the form of a home invasion.

The support worker said Dillon had reported the incidents to police and provided the service incident reports and reference numbers.

But the inquest heard those documents were not in the materials before the court.

The support worker said Dillon told him he was once a "bad guy, a horrible man".

He was proud of being a hard man who lived on the streets and grew up abused.

But Dillon claimed to have changed, turned over a new leaf and become the father he always wanted to be.

"He could really talk, he could really talk," the support worker said.

But the support worker said while he believed Dillon would harm anyone who laid a hand on his boy, he believed he would never hurt the boy.

The inquest continues.