During a 45-minute telephone conversation two nights before he fatally stabbed Miss Elliott, Weatherston kept going "on and on" to a previous girlfriend about the 22-year-old honours student, criticising her and saying he could not believe how he had let someone with such a negative attitude into his life, the witness told the court.
The woman, whose identity is suppressed, said she tried to tell Weatherston that Sophie was young and had a lot of growing up to do, but he "wouldn't let it go and kept going over and over it".
He was obsessed with Sophie and with his application for an economics lectureship.
He was concerned about the impact Sophie's association with Dr Robert Alexander, her honours course supervisor, was having on his ability to get the position.
The woman, who had been in a relationship with Weatherston for several years, said he was - in general - a kind, generous and highly motivated person, who was obviously very intelligent.
She thought him, initially, to be of very sound character.
But at times he could have a very nasty streak.
He had called her names, told her she was stupid and, at one point, "undesirable" to him.
She had never raised her voice to him.
In the latter part of 2006, he had assaulted her, kicking her on the back and ribs as she sat on the floor.
He then jumped on her back and shoulders with "a lot of force", causing her knee to strike her eye and nose, resulting in a bleeding nose and a bruised eye.
"I got frightened and started yelling at him to keep away from me," the woman said.
She said she ran into the bathroom, yelling at him not to come near her as she cowered in the far corner of the room.
Weatherston locked the door of the house and took her car keys so she could not leave.
He said he "wanted to talk about it".
She told him she thought he needed some help, that he could not continue with such behaviour and she would leave him if he did not get some help.
During 2007, she was often away from Dunedin and her relationship with Weatherston ended.
She was very distressed about it, but they remained friends.
She later met Sophie, whom the accused had told her about in August 2007.
She encouraged Weatherston to invite the young woman to his December graduation dinner and party, although she knew it would have been difficult for her because she [the witness] was also there.
When she was in Dunedin again around New Year, "a common strand of our conversations" - as it had been for several months - was Weatherston's concern about whether Sophie had said anything to Dr Alexander about her allegations of violence and abuse by him towards her and about how awful she was.
