Sophie Elliott began referring to ex-boyfriend Clayton Robert Weatherston in her diary as "Norman Bates" - the villain from the film Psycho, his trial was told today.

Weatherston is being tried in the High Court at Christchurch for Miss Elliott's murder in a knife attack at her home in Dunedin on January 9, 2008.

Erin van der Water told the court today of Miss Elliott's relationship with Weatherston and a violent incident on December 27, 2007, that Miss Elliott recounted to her, in which she said Weatherston had pressed a forearm across her throat, Christchurch's Court News website reported.

Cross-examined by defence counsel Judith Ablett-Kerr QC, Miss van der Water was told that Miss Elliott had referred to Weatherston in her computer diary as "Norman Bates" after she had severed ties with him. She said that Miss Elliott said it was how Weatherston had referred to himself.

She said she was surprised to hear that Miss Elliott had gone to see university tutor Weatherston at the university on January 7, 2008. She had warned her quite strongly not to have anything more to do with him.

Miss Elliott said Weatherston had put an arm around her and taken her into the office where they argued.

He said there was no point in telling anybody about the December 27 incident because she was clearly crazy, a liar and had made it up, and nobody would believe her. He denied that anything had taken place - she had made up the whole incident, Miss van der Water told the court.

An earlier girlfriend of Weatherston's - who has name suppression - told of having a relationship with him through to about August 2007.

She said he was generally kind, generous, highly motivated and driven but could also have a nasty, mean streak. He would sometimes say demeaning things to her and she recounted an assault by Weatherston in the period from August to October 2006.

She said the couple were arguing and she suggested they should "just call it quits". Weatherston kicked her in the back and ribs. She was kicked across the room and he then jumped on her neck and shoulders.

Her knee went into her eye and her nose started to bleed. There was a mark above her eye.

She felt frightened and yelled at him to stay away. She ran into the bathroom and wanted to leave, but Weatherston locked her in and grabbed her car keys.

She told him she thought he needed help about his behaviour and insisted that he went to counselling.

She said there was no intimate relationship between them at that stage and there had not been for quite some time.

He told her in August 2007 that he was seeing Miss Elliott, at the time he broke the relationship off with the witness. She remained in contact with him. He indicated that his relationship with Miss Elliott was not going well. He said she was "showing her mean streak" quite a lot.

She recalled a phone call from Weatherston in early January, 2009, when he said Miss Elliott had visited him to pay for glass she had broken in his door. He said Miss Elliott had hit him in the head or neck with her elbow. "He was extremely upset or irate about it."

She also said Weatherston was earlier upset about how long he had let the destructiveness of the relationship with Miss Elliott continue.

The trial is proceeding before Justice Judith Potter and a jury.