Murder-accused Clayton Weatherston was unable to stop stabbing his ex-girlfriend because he had lost control, the defence has told a High Court jury.
The former University of Otago tutor denies murdering student Sophie Elliott by stabbing or cutting her 216 times at her family's home in Dunedin.
The 33-year-old has admitted a charge of manslaughter.
The Crown says the attack on Miss Elliott, 22, in January last year was deliberate and premeditated.
But the defence argues that Mr Weatherston lost control, was provoked into killing Miss Elliott and is therefore guilty of manslaughter, not murder.
On Monday, lawyer Judith Ablett-Kerr, QC, told the Christchurch jury that Mr Weatherston was provoked by a torrid and tumultuous relationship with Miss Elliott - a relationship she said the accused was ill-equipped for because of his particular make-up.
The court was told when Mr Weatherston went to Miss Elliott's house he was coiled like a spring. Once the pair were in her bedroom she lost the plot, swearing at the accused and attacking him with a pair of scissors.
Mrs Ablett-Kerr said manslaughter was the appropriate verdict, as Miss Elliott provoked Mr Weatherston to lose control.
She said it was the straw that broke the camel's back and Mr Weatherston's response, although horrific, was spontaneous.
"He went on stabbing this young lady long after she was dead. That's not the action of a man who the Crown would say was normal and who was not out of control."
The court was told Mr Weatherston suffered from a personality disorder and narcissism which did not allow him to show empathy.
In her closing submissions, Mrs Ablett-Kerr said evidence given by Miss Elliott's mother was unreliable.
Lesley Elliott previously told the court that she heard her daughter's screams coming from the bedroom. But Mrs Ablett-Kerr suggested that the traumatic events Mrs Elliott experienced had clouded her account of what happened that day.
The comment drew gasps from the Elliott family, two of whom got up and walked out.
Deliberate decision made to kill - Crown
Prosecutor Robin Bates summed up the Crown's case earlier on Monday, telling the court there was no provocation and that Mr Weatherston made a deliberate decision to kill and mutilate Miss Elliott.
He said the defence suggestion that Miss Elliott had attacked Mr Weatherston with a pair of scissors was illogical and not supported by evidence.
Mr Bates told the jury Mr Weatherston had tried to portray himself as a victim, but had repeatedly rewritten situations to suit his purposes.
The Crown alleges Mr Weatherston had made up his mind to kill Miss Elliott when he locked the door to her bedroom to carry out his plan.
The court was told he showed no remorse after the attack.
"Almost everybody in this court would turn back the clock. There's no indication from this accused that that's what he would do. The Crown says he is still saying, 'This was Sophie Elliott's fault, she caused this.'"
Justice Potter will sum up the case on Tuesday before the jury retires to consider its verdict.
