A university worker stabbed his boss 15 times out of "jealousy" because she rejected him, not in the haze of a depressive illness, a court has heard.
David Browning knifed Jillian Howell in the chest, neck and abdomen after the pair spent the evening of October 26 at her home in Sandgate Road, Brighton.
She was found with the word "bully" scrawled on her head.
Her 52-year-old assailant denies the attack was murder, saying his actions were instead the result of a debilitating mental illness.
But, at the conclusion of a trial at Hove Crown Court, the prosecution rejected his defence of manslaughter on the grounds of diminished responsibility.
Prosecutor Alan Gardner said Browning was a spurned admirer, someone "deeply self-centred, selfish, a man with a vindictive streak".
He said during his closing argument: "He offered, we know, no explanation for why he did it, only to say 'it must have been my depressive illness, that must have caused me to make a criminal decision to kill Jillian Howell'.
"We, the prosecution, say no, the evidence points to a very different reason, to this being a man who had a stable life jolted by the death of his father.
"A man who found himself in an emotional crisis, a man who found a sympathetic ear for his issues, several years younger than him, an attractive single woman.
He added: "This was a crime driven by those feelings ... of anger, jealousy, betrayal, those sort of things."
His defence counsel, Graham Trembath QC, responded: "The context must surely be they met three times (socially). If he began to entertain notions of a potential romance arising from three meetings, was it the depressive illness that substantially impaired his ability to think?
"Yes, there was an emotional attachment. It wasn't a romantic matter, it is because, in his depressed state, severe severity, there was that fatal, as it turned out to be, fatal connection."
The defendant - nicknamed Spock - suffers from depression, but two psychiatrists gave differing assessments of its severity, the court heard.
One felt the diagnosis was serious enough to have rendered him incapable of making a rational decision, while the other said he was still able to function in day-to-day life.
His behaviour on the night of the killings was "bizarre, very bizarre", Mr Trembath said.
This, coupled with a virtually unblemished past, suggested a bereavement had triggered a depressive episode, he said.
The defendant's father died aged 73 in October 2016 when he fell off a ladder.
"There doesn't seem to be any dispute that he was perfectly fine, he was living his life, everything was perfectly ordinary in his life. He had not been in a fight, not lost his temper, nothing at all, and then witnessing the attempt to resuscitate his father had an impact, a heavy fist that hit him straight in the face," Mr Trembath said in his closing argument.
The married father of two is said to have formed an intense attachment to his superior at the University of Brighton and confided his emotional problems to her.
It was previously heard he became "possessive, controlling and jealous", while she felt compelled to help him as she had experience working with suicidal people.
The defendant subsequently claimed the pair had clashed and that he was unhappy with her management style.
He also allegedly sprayed graffiti on the walls of the crime scene, which tried to frame her close friend Sean McDonald.
Distressing details of Ms Howell's final moments were previously described by Browning in court.
He confided his planned suicide to her and feared she would attempt to get him sectioned, prompting him to plunge a knife into her back as she tied her laces.
The Samaritans volunteer screamed "you bastard" and tried to grab the knife, Browning claimed, but he continued to stab her and replied: "I'm sorry Jill, this is what mental health does to you."
He stayed in the house for up to six hours before dialling 999, Mr Gardner said.
Officers found him outside the police station, where he told them: "In a nutshell, I have killed my boss."
The defendant, of Willow Drive in Seaford, East Sussex, denies murder but admits manslaughter by diminished responsibility and possession of a knife in a public place.
The trial continues.