BBC News Published media captionShort films about the mothers' experiences have been released by the Met Five mothers have relived the 'hardest' phone calls they each had to make after their sons were stabbed to death - in a bid to urge Londoners to speak up about knife crime. They have shared their stories as part of a Hard Calls Save Lives campaign, which has been launched by the Met Police. The Met say the campaign is particularly aimed at encouraging mothers, sisters or aunts, whose children, siblings, nephews or nieces may be on the fringes of knife crime to make a report if they know someone who carries a weapon or where one has been hidden.