A suspected serial killer dubbed the Scalp Hunter is linked to seven murders. John Sweeney , 66, is already serving a whole life sentence for killing and chopping up US-born Melissa Halstead, 33, and mum-of-three Paula Fields, 31. He also attacked ex Delia Balmer with an axe at her London home in 1994 but she survived. The London nurse, played by Anna Maxwell Martin in the gripping new ITV drama Until I Kill You , lived with Sweeney unaware he was a killer. Delia managed to escape the