A man who stabbed and bludgeoned a Dunedin couple to death has not yet explained why he killed them. 

Wiremu Paul Namana (50), a former youth social worker, appeared in the High Court at Dunedin yesterday where he was sentenced to life with a minimum of 17 years' imprisonment over the murders of 49-year-old David Clarke and 35-year-old Anastasia Neve in January 2018. 

Justice Gerald Nation accepted the defendant might want to block out his actions but refused to accept the man did not remember the episode. 

Wiremu Namana was sentenced to life in prison for the 2018 murder David Clark and Anastasia Neve in their South Dunedin home. (Photo / Christine O'Connor) 

"You killed two people in an extremely brutal attack. Callously, you set fire to their bodies; in doing so you set fire to their home in a way that put an immediate neighbour in extreme danger. You did that to cover up what you had done," he said. 

Ms Neve's sister Krysta described an overwhelming sense of ''terror'' when she discovered her sister had been murdered. 

''She didn't deserve to die and she didn't deserve to die in the way she did,'' she said. 

Another sister, Megan, spoke of her sadness that her new child had been robbed of the chance to know her auntie. 

She said she would remember Ms Neve as ''an amazing artist with incredible handwriting'', a lover of poetry and music. 

After repeated denials, the defendant finally admitted the double murder-arson in June. 

Namana had been addicted to morphine and his drug debts were spread so widely he was struggling to find a supplier. 

His life was in freefall, the court heard. 

Hours before the murder he had complained to a mate about withdrawal symptoms kicking in and had broken up with his long-term partner. 

When Namana could not get in touch with Ms Neve and Mr Clarke, he went to the couple's Wesley St flat and ''flew into a rage'', court documents said. 

Using a cricket bat, knife and a mini sledgehammer, he attacked them, inflicting devastating injuries. 

Ms Neve suffered 14 stab wounds as well as blunt-force fractures to her head. 

Mr Clarke was similarly savaged, with extensive facial fractures and knife wounds including one which penetrated his brain. 

Within hours, Namana returned to empty a five-litre petrol can in the victims' bedroom and set it alight. 

Over the ensuing days, a bizarre and confusing series of interviews with police unfolded as he tried to shirk responsibility. 

Anastasia Neve and David Clarke. (Photo / Supplied) 

Crown prosecutor Craig Power said Namana had an ''uncontrollable anger'' and noted both victims were much smaller than the defendant. 

''When he attacked them they had no chance,'' he said. 

Defence counsel Judith Ablett-Kerr QC detailed her client's background, which involved significant trauma, compounded by the use of alcohol and drugs from the age of 10. 

She described it as ''a genuinely dreadful existence'', and told the court he set fire to school classrooms when aged 7, sparking the intervention of social services.