Mark Ryan, 32, as 'an act of love' helped Suzanne Winson, 25, to dispose of evidence after she battered a 78-year-old man to death with a spanner, said Richard Horwell, for the prosecution.
Winson, jailed for life last month after being found guilty of murder, came to his house covered in blood on the day of the killing - 16 December last year. According to Ryan, she said: 'Can I trust you? I think I've done somebody.'
Ryan, her mother's longstanding boyfriend, told police: 'I love the girl, everyone classes me as her grandad.'
Winson asked Ryan to help her to get rid of the clothes she was wearing. Ryan gave her a bin bag and waited in a park for two hours while she threw the incriminating evidence in the Thames.
'He was acting out of feelings of protection towards someone he was particularly fond of,' said Mr Horwell.
Ryan told police he was unaware that hours earlier she had left James Coade dying in a pool of blood at his house in Page Street, Westminster. Winson was a frequent visitor to Mr Coade's home. She killed him for his pounds 160 pension money.
Ryan, of Kingswood Road, Fulham, pleaded guilty to perverting the course of justice.