"When he died, part of me died with him, I know with certainty it happened for his sister, his brothers and his mother too," the Rose Tattoo rocker told the NSW Supreme Court on Tuesday.

The Anderson family would forever be denied Liam's amazing warmth and love, his laughter, the sight of him slouching in a chair and asking him if he wanted a cup of tea, he said.

"I am condemned, as we all are, to sadness."

Mr Anderson said he'd given a piece of his heart to each of his four children and Liam's death in November 2018 - at the hands of his psychotic best friend Mathew Flame - had provided a full understanding of the phrase "a hole in one's heart".

"(Liam) took a part of me - the part he, and only he, had with him," Mr Anderson, whose real name is Gary, said.

Flame, now 22, was last month found guilty of manslaughter after a jury accepted the psychosis that caused him to believe his mate was a demon stemmed from the severe mental illness of schizophrenia.

Mr Anderson said he'd never forget his son Galen telling him "something terrible" had happened to Liam.

"These terrible words reverberate in my head daily and will, I imagine, for the rest of my life," he said.

"Arriving home some hours later lost in shock, (I recall) the haunted look in my children's eyes, the pain, the helplessness, the anger and the overwhelming grief."

Mr Anderson was on the verge of tears for much of his victim impact statement.

But he hardened briefly, as he told the court time would never erase the way his son died "or by whose hand".

"Darkness ... lurked within him (Flame) waiting for release," Mr Anderson said.

"I believe that darkness still resides there."

Liam's mother Lindy Anderson explained her hugging of Flame upon the jury's verdict was out of a desire to find peace.

Having barely functioned in the year after her son's death, she said she still feels as though she's drowning in a shipwreck, surrounded by fractured reminders of the beauty of what was.

"All I can do is try to stay afloat," she told the court.

Liam's eldest sibling Roxanne said her best mate in the family was a "lover, not a fighter", who was also funny, creative and fiercely loyal to those closest to him.

"His best quality was what cost him his life," she said, referring to how Anderson had been trying to help his psychotic friend before the fatal attack.

Flame took his 10th MDMA capsule of the night about 5am - about an hour before bashing his mate to death.

His barrister tendered a bundle of documents including a paper on chronic tolerance to MDMA and a letter from Flame outlining his remorse for what had occurred.

"From any point of view, this is a very tragic case," John Stratton SC said.

An earlier incident in which Flame also mixed cannabis and MDMA use and then believed his colleagues were demons was "of a very different nature", he said.

The Crown accepted Flame was remorseful but said it differed from a full acceptance of responsibility, which would involve remorse for his "excessive and reckless consumption of drugs".

Justice Richard Button will sentence Flame on December 16.

Australian Associated Press