Nor did he realise the depth of the ill-feeling his actions had aroused.
The evidence came from the psychiatrists immediately afterwards that might have explained it.
They spoke of narcissism and obsessionality.
Those who saw his performance as he gave evidence in his defence, must have seen that Weatherston believed he had charmed people while he held a national audience.
Much of his evidence was available on television and media websites, giving people an up-close-and-personal look into the behaviour of a man whose actions were too difficult to understand.
There were some slight insights for those watching, such as when the 33-year-old Otago University tutor was talking about a gathering at the Zucchini Brothers restaurant in Dunedin.
His mother was there, and she had apparently found it a difficult sort of environment.
People of her age group were not much in evidence, he explained to the court, in an academic sort of way.
But he declined to comment publicly on his mother's age.
"I think I'm in enough trouble here," he said, with a self-effacing sort of smile.
It was as though he was talking about bunking class for the afternoon, not being on trial for his life, for the life he took when he stabbed his ex-girlfriend Sophie Elliott 216 times.
He was admitting manslaughter, but the crown was insisting on murder.
The ill-feeling stemmed not only from the grotesque stabbing, where he aimed for her eyes, ears, face, cut off her nose, cut off a nipple, mutilated her genitals.
It was also about how he then wished to shift the blame onto her and blacken her name with his defence of loss of control through provocation -- as if there could be a rational reason for someone to do what he had done.
The defence did not characterise it as a frenzy. It was done in a measured way. In his opening address for the defence, Greg King described the results of this loss of control as "an irresistible impulse".
A normal person may have resisted. The argument in Miss Elliott's bedroom -- a clash that was nothing out of the ordinary for this couple -- might have resulted in harsh words, a slap, perhaps a punch for another pair.
But in this situation, with the peculiarities of Weatherston's psychological make-up, the defence argued that it led to disaster.
He had gone there not expecting this, they said. He went to the door not expecting her to be home -- her car was not in sight -- and planning to return gifts as a gesture that finally severed the relationship.
Instead, it degenerated into an argument about her infidelity in Australia, and he flung the question at her -- did he need to take a medical test for a sexually transmitted disease? On his account, she lost her own control at that point and came at him with scissors, knocking off his glasses and leaving him vulnerable and exposed.
The defence account of what must have happened during the time that Weatherston cannot remember, is that he got the knife -- the knife he carried for protection on campus and for slicing fruit for lunch -- out of his bag and the terrible attack began.
That must have presented the jury with a few problems: the fact that he went there with a knife was difficult enough, and the fact that even without the glasses that he said he did not find until later, he was easily able to find the knife in his bag and hit his targets with precision.
There was also the lead-up. At one stage Miss Elliott came downstairs from the bedroom to the kitchen, and spoke to her mother, Lesley Elliott. She said that Weatherston was just sitting there and saying nothing.
That must have seemed to the jury rather like someone working himself up to something.
Lead defence counsel Judith Ablett-Kerr QC tried to shut off those kind of ideas with a closing that cited Mrs Elliott as an unreliable witness because of the trauma she had seen.
It was too much for some in the court. There was gasping and two Elliott family members or supporters got up and left from the public seats.
The families have been stunned by the unfolding story in the courtroom.
Weatherston's mother has seen a side of her son she had never expected. The psychiatrists say it is not unusual for someone with Weatherston's character to display respect to someone like his mother.
Weatherston was driven, in his university work where he was ultra-competitive, and in his relationship where he says Miss Elliott kept controlling him and making comparisons.
The defence was that he was driven to distraction.
The jury didn't buy it.
- By David Clarkson for NZPA
