I was once asked to give evidence as an expert witness at a murder trial. The defendant was found guilty of murder and sentenced to 20 years in prison. He did actually kill the woman but I am not persuaded that he intended to murder her. They were involved in ‘knife play’ and he was terribly drunk. His hand slipped and she died. It did not help his case that he was heard in the garden, that same afternoon, shouting, ‘I will kill you, you bitch’.