A man has been jailed for at least 20 years for the frenzied stabbing murder of his drinking mate at Thevenard near Ceduna on the west coast of South Australia.

The Supreme Court heard Barry Walter Coleman, 39, slit the victim’s throat and stabbed him more than 30 times, in November 2012.

Earlier, the men were seen drinking amicably at a local hotel.

Coleman pleaded guilty to manslaughter and claimed he acted in self-defence, but a jury rejected that and convicted him of murder.

Justice Michael David says it is hard to understand why Coleman attacked his 33-year-old friend.

“The circumstances of the offending and why you committed this offence are indeed a mystery, [as] you have no previous convictions for any form of violence, there is no suggestion you are the type of person who would behave the way you did,” he said.

“Until this incident, you were a well-liked individual with no history of violence. It is very hard to understand what can only be described as a frenzied and violent attack.

“The deceased suffered some 34 stab wounds to his body including a slit throat. Both of you were obviously very drunk.”

Justice David spoke of the killer’s intellectual impairment.

“You are, to a certain extent, intellectually disabled … nevertheless you are fit to stand trial and you are [deemed] mentally competent to commit a criminal offence.”

Justice David says Coleman’s mild intellectual disability would have exaggerated the effects of alcohol he consumed.

He says an apology from the killer was “heartfelt”.

Coleman has been in custody since the stabbing and his 20-year non-parole period has been back-dated to that time.

The victim’s identity has been suppressed by the court.