The parents of convicted murderer Daniel Jack Kelsall, 22,  believe that if he did kill Morgan Huxley then the doctors he confided in about intrusive thoughts of stabbing had let him down.

Last week Kelsall was sentenced to a maximum of 40 years imprisonment for indecently assaulting Huxley and stabbing him to death as he lay in his Neutral Bay unit.

"If he'd got that help before it might never have happened," his father Mark Kelsall said.

"They [the doctors] could have scheduled him or – and if he's guilty it would have saved that boy's life and it would have saved the potential of what everybody has had to go through.

"For a person to have stuck his hand up so many times to say 'I need help,' and to end up where we all are – is appalling."

Mr Kelsall  said that he believed the medical professionals, who all diagnosed his son with different disorders, had let him down and most of all, let down Morgan Huxley.

"We wonder whether we've been let down."

Just 18 months before Kelsall murdered Mr Huxley he told his adopted parents, his GP, a psychiatrist  and a psychologist that he did not feel right on the medication he was on – a drug named Seroquel.

He was later taken off his medication,  prescribed fish oil and told to meditate.

"Now if [a psychologist] has got a guy who said he was carrying a knife around, that he feels like stabbing people, seen him 10 times, why the frig did he take himself off his medication?" he asks, throwing his hands in the air.

The Kelsalls do not talk about whether they believe their son is guilty of stabbing Mr Huxley to death the day after the federal election in September 2013.

"It's assumed that we wanted Jack found not guilty - that's not the case - we want the truth, that's all we want," he said.

The New Zealand-born couple, who live in Neutral Bay, also said they have never asked their son if "he did it" but he has told them he is innocent on the rare occasion.

"He has just said a couple of times he didn't do it - but I wonder in a way whether he was trying to protect us," his mother Lynne Kelsall said.

They say they don't believe he is capable of such a violent murder but if he is guilty, they want him to get the help he needs.

"If he did do it, and I'm not suggesting he did or he didn't do it, then he needs a huge amount of help. He needs help, one way or the other," Mrs Kelsall said.

She said the first thing her son said to her after he was sentenced was, "Are you all right?". He then hugged his father and thanked him for making a speech on the courthouse steps acknowledging the grief the Huxleys will endure for the rest of their lives.

"We feel for the Huxleys and that's not just lip service, that's genuine. We can't imagine where they are at. In some ways we've had a loss but nothing like theirs," Mr Kelsall said.

The Huxleys have previously said Morgan, a talented marine engineer, was stolen by a "worthless psychopath" and they will forever be living a life sentence without him.

During his sentencing at the NSW Supreme Court on Wednesday Justice Robert Allan Hulme said Kelsall had shown no remorse and continued to deny his guilt.

"It was utterly senseless and needless. It must have been the doing of a very disturbed individual," Justice Hulme said

Lynne and Mark Kelsall say they love their son and will support him forever and will continue to visit him twice a week as they have been doing since his arrest in October 2013.

"He's respectful, loving, caring, non-judgmental, hard-working, considerate, generous, untidy, loves reading all day everyday, loves maths and problem solving, physics, loves his pets, really passionate about cooking," Lynne said.

His father shakes his head and said his son was a great mate who spent a lot of time with him as he worked from home out of his Spruson Street unit.

The Kelsalls stressed their decision to speak about their son was not to cause the Huxleys any more grief but in the hope people with mental illnesses get the help they need.

If their son had, they believe two families would still have their boys.

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Apology to the Huxley family

Fairfax Media apologises to the Huxley family for distress caused by this story. As stated in the story, Daniel Jack Kelsall was sentenced to 40 years in prison for the murder and indecent assault of Morgan Huxley. Fairfax Media apologises for any interpretation from the story that the court’s finding of murder was in any way in question in the general community. The story should have also said that despite a number of assessments by psychologists and psychiatrists, none gave a confirmed diagnosis that Kelsall suffers from a mental illness. The judge found none of Kelsall's mental health issues were significant enough to reduce his sentence.