A naked man seen walking around like a zombie had beheaded his mother because he thought she looked like a witch, the Old Bailey heard.
Daniel Coriat, 44, was arrested hiding in a wheelie bin at a local train station.
He told police he was the son of God and had been living in the bin since coming down from the sky, said Sarah Plaschkes QC, prosecuting.
Coriat, of Forest Hill, south London, pleaded guilty to manslaughter on the grounds of diminished responsibility.
Elizabeth Coriat, 76, was found on her bed at the flat they shared in March, last year.
She had been mutilated and decapitated with various weapons.
Mrs Coriat had told an advice worker that her mentally ill son could turn nasty when he was not taking his medication.
Miss Plaschkes said Coriat was seen completely naked outside the flat the morning after his mother was last seen alive.
"He had a blank, vacant stare. He was walking like a zombie." she told the court.