Benjamin Maxwell, 30, died after being stabbed 18 times to the chest and arms by Smillie on December 25, 2012.

Smillie wounded Ashley Stott by stabbing him four times to the back and arm during the altercation.

The accused was found guilty after a Burnie jury rejected a self- defence argument.

The court heard that Smillie was in the area to swap Christmas gifts with his partner shortly before the incident and had parked his four-wheel drive, in which he was living, outside Mr Stott's unit.

The events that then led up to the trio's fight were unclear, Justice Stephen Estcourt said in Hobart's Supreme Court yesterday.

"It may have been Mr Smillie had declined to take Mr Stott and Mr Maxwell to the bottle shop ... it may have been Mr Smillie was jealous of the two men suspecting they had been involved some way with his partner," he said.

It was also unclear how Smillie had come to stab Mr Maxwell, he said.

"I'm satisfied that it was clear from the type of knife used and the very large number of stab wounds inflicted on Mr Maxwell ... he must have known (it) was likely to cause death," he said.

Victim impact statements from Mr Maxwell's mother and Mr Stott were tendered to the court.

"The death has had a highly debilitating effect on his mother, who's never recovered from the shock of her son's death," he said.

"Mr Stott suffers ongoing psychological problems as well as the effects of his physical injuries."

Justice Estcourt said Smillie had a difficult upbringing and had been diagnosed with schizophrenia.

A forensic report was unable to say what role, if any, Smillie's psychiatric disorder played in his wrongdoing.

However, Justice Estcourt said there was no suggestion that Smillie was not legally responsible for his actions.

"Mr Smillie expresses no remorse for his conduct but I do take into account that his failure to accept responsibility may be attributable to the effect of his psychiatric disorder," he said.

Justice Estcourt sentenced Smillie to 21 years' jail with a non- parole period of 12 years.