Clayton Robert Weatherston says he has no memory of stabbing or mutilating his ex-girlfriend Sophie Elliott - apart from one stab into her throat with a pair of scissors.
On his third day in the witness box, Weatherston today gave his account of the minutes in Miss Elliott's bedroom in Dunedin when he stabbed her to death.
He said he could not remember using the knife he had taken to her house on a visit he said was planned only to return some of her gifts as part of their break-up.
Weatherston told the jury in the High Court at Christchurch that he "wanted to get the moral high ground".
He repeatedly said he could not remember or could not recall what happened in her bedroom after he said she attacked him with a pair of scissors during an argument.
But he said he did remember putting his hands around her neck and trying to push her away, at a time when his glasses were knocked off.
Weatherston told the court he carried a knife in his bag for security, because of concerns around the Otago University campus where he worked.
He said he had no intention of killing Miss Elliott when he went to her home about midday on January 9, 2008. It was the last thing he would have thought would have happened, he said.
"I was looking forward to walking away and moving forward," he said.
"I wanted some type of mana, but what happened was the opposite self-destructive thing."
He said had no recollection of using the knife, but he did recall one blow with the scissors at the end of the attack.
Weatherston said he remembered a feeling of huge stress and anxiety, and being disoriented and falling on top of Miss Elliott.
He recalled standing over her with a pair of scissors in his right hand and the scissors had gone through her throat, meeting some type of resistance.
"The crunching feeling is quite vivid."
He said he stopped what he was doing and leaned back against the bed.
Cross-examined by crown prosecutor Robin Bates, Weatherston said that hearing all the evidence did not make him remember what had happened. He said he would rather know the answers.
Weatherston suggested that the alleged attack by Miss Elliott with the pair of scissors could have been "the straw that broke the camel's back".
"You reacted and you killed her," said Mr Bates.
Weatherston replied: "The jury can believe what they want. I just want to explain the situation. That is my goal. If I did something wrong, I would tell you. I take responsibility for things."
In evidence earlier today, Weatherston denied he pushed her down the stairs at the university as she claimed.
"It was a public area. It was too ridiculous to comprehend but I may not be entitled to such views considering the position I am in," he said.
He claimed Miss Elliott elbowed him in the throat in one incident.
She had said it was payback for an earlier attack, but he said she had struck him and he had grabbed her wrists and they had ended up on the bed.
Weatherston told the jury he followed Miss Elliott to her car afterwards and made a comment about her recent trip to Australia.
He said he told her: "If your plane had crashed I would never have had to deal with any of this shit."
Weatherston said that before the fatal attack he had not been sleeping or eating and had been taking four times the amount of anti-depressant medication he should have.
Cross-examined, Weatherston said he had no recollection of the mutilation of Miss Elliott.
He said he only deduced he had used the knife because he had a cut on his hand. He told the court he did not recall locking the bedroom door.
