Justice Natalie Adams sentenced Warren Anthony Scott, 39, for a minimum term of six years in the NSW Supreme Court on Wednesday for killing Edward "Eddie" Carter at his mother's Eden home in April 2019.

The Crown had argued at the Bega man's judge-alone trial that Scott lost control due to excessive alcohol consumption which usually preceded him going off medication for schizophrenia.

But Justice Adams found it was this longstanding mental illness that caused a psychosis that he was unable to explain due to his intellectual impairment.

"The objective facts are very grave," Justice Adams wrote in her sentencing remarks.

"The deceased was stabbed 31 times in his own home after being detained for at least an hour by the offender during which time the latter was wielding a knife and menacing him."

Mr Carter's daughter Tina Sahin told the court her father was a "happy gentle soul that would not harm a fly" and her family had been ravaged by the loss.

"Warren Scott's choices to not be responsible or accountable for his own mental health has changed our family forever," she said.

It is believed Scott was drinking in a park daily for about two weeks leading up to the incident.

At the time he was already subject to an intensive corrections order for a similar unprovoked attack on his mother after bingeing on alcohol, but refused help and rehab.

Scott admitted he stopped taking medication for paranoid schizophrenia, diabetes and epilepsy when drinking daily for long stretches.

On this day the usually "happy laughing" jokester appeared very different with a blank stare that "freaked" family friend Kevin Dixon out.

A teetotaller, Mr Dixon had driven Scott home "hundreds of times" but "he wasn't Warren" the final time he was in his car, he said in evidence.

The following day Ms Scott, Mr Carter and her son began drinking early and listening to music, "having a good time," Scott testified.

But without warning, he suddenly jumped up, retrieved "the biggest knife" from a kitchen drawer, and held it to his mother's throat full of rage.

After lunging at her a second time she fled, leaving Mr Carter captive in the home with Scott.

An attending police officer said Scott drew the curtains at one stage to hide the hostage situation and continuously yelled "f*** off pigs go away," to their questions.

An "emotionless" Scott was later seen holding the blade right between his victim's eyes before thuds were heard travelling around the house.

After Mr Carter yelled he had been stabbed Scott could be heard saying he would watch him "bleed out".

His mother had seen her son drunk countless times but never looking and sounding "possessed ... something evil you see in a movie, the way he looked the way he sounded just so evil".

"I am satisfied the accused's capacity to understand events and judge whether his actions were right or wrong and to control himself was substantially impaired at the time of stabbing," Justice Adams concluded.

Upon release Scott will need lengthy supervision to ensure he remains alcohol-free and continues on his medication, she said.

Australian Associated Press