How one of the first Tesco Clubcards was used to pay off a blackmailer threatening to poison frozen food. And how that Clubcard was used to catch him.Presented by journalist and true crime documentary maker Amber Haque and criminal psychologist Dr Julia Shaw.Producer: Ciaran Tracey with help from James Shield Executive Producer: Innes Bowen Production Coordinator: Juliette Harvey Mix Engineer: John Scott Commissioning Editor: Dylan Haskins Assistant Commissioner: Izzy Lee-PoultonBad People is a BBC Studios production for BBC Sounds