Joanna Yeates's killer claims he simply "misread" the situation when he strangled her, the murder trial heard yesterday.
Vincent Tabak's barrister insisted that the defendant had first tried to kiss the 25-year-old landscape architect and that her death was a tragic misfortune caused by her horrified reaction.
While condemning his client, who admits manslaughter but denies murder, as "calculating" in his attempts to cover up Miss Yeates's death, William Clegg QC insisted he had never intended to kill her.
The jury at Bristol Crown Court had heard how she had been strangled after returning home from Friday night drinks with colleagues on 17 December last year, and suffered 43 injuries.
In the first description of Tabak's version of events, Mr Clegg said it was "pure chance" that the two neighbours, who were virtual strangers, were home alone. Mr Clegg insisted the young woman had been "bored and lonely" with her boyfriend away.
The 33-year-old Dutch engineer had walked past her kitchen window and she invited him in, marking, the QC said, an "unfortunate starting point for the defence case".
"She said that her boyfriend was away and she was alone and he said that his girlfriend was away and he was alone," the lawyer said. "And as the two of them talked inside that flat, Vincent Tabak completely misread the situation that he had walked into... He misread her friendliness towards him and made a move towards her as if he was about to kiss her on the lips."
As he put his arm around Miss Yeates, she screamed and he put a hand over her mouth, Mr Clegg continued. "He said to her 'stop screaming'. He apologised and said he was sorry.
"He took his hand away and she carried on screaming. He panicked. He put one hand around her throat and the other over her mouth. In seconds – far less than a minute – Joanna went limp. She was dead."
The court heard earlier how Tabak had searched the internet almost hourly after disposing of the body. He watched a time lapse video of a decomposing corpse, searched for definitions of "sexual conduct" and "sexual assault", researched the average sentences for murder and manslaughter and examined the unsolved murders of Melanie Hall and Anni Dewani.
Mr Clegg added: "Despite the awful secret he was carrying, he tried to carry on as before, going to dinner parties, going to work, living with his girlfriend and living a lie."
The trial continues today.