The man accused of killing Walton business woman Kate Beagley says she stabbed herself to death.
Karl Taylor, 27, from Kemble Street, Covent Garden, said Miss Beagley killed herself after she drank a bottle of wine with him on a bench in Richmond Hill.
The fitness trainer admitted he had a knife up his sleeve because he had felt suicidal.
He said the knife fell out when he bent over and that he put it on the bench.
He then picked up his mobile which was ringing but was distracted by a scrape' which was Kate picking up the knife, the court was told.
"My attention was drawn to Kate. She was standing up and had the knife in her right hand. She was crying profusely," said Taylor.
He said he asked her "Do you want me to give you that knife?" and she said "No".
"She said I love my mum, I miss my mum and kept mentioning the name Fraser," said Taylor. "She was gesturing a lot and brought the knife to her face a lot of times.
"She prodded herself with the knife and was moving her neck towards the knife."
He added: "I was startled and very stunned."
After checking Kate's pulse and realising she was dead, Taylor said he lay down next to her on the grass.
He said he did not ring the emergency services as he knew she was dead and that the police would think he was responsible.
He picked up her body and put her in the boot of her car after failing to get her into the front and back seats, the court heard.
Asked why he did not leave her body in Richmond Hill, he said: "I felt an affinity with her. I felt partially responsible."
He went on to say of Kate: "She had a dark and cold side and I felt that overtake her and overwhelm her. I then felt I had the responsibility to do something with her."
Taylor told the court that he had stripped Miss Beagley before leaving her in woodland near Watford because he had wanted her "to feel pure".
He told the court that as he left her body he saw Kate as an angel who was going to go to heaven.
In response to a pathologist's findings that Kate had "classic defence wounds", Taylor said: "They could have been caused by her picking up the knife by the blade."
Miss Beagley, 32, from Nelson Close, was found dead in woodland in June last year. She had been stabbed 31 times in the face, neck and throat.
Taylor denies murder and the trial continues.
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