How to deal with the blackmailing?

My best friends ex-fiance clicked her nude photograpes on skyp,she requested him to delite them but he is not doing so infact she is afraid that he has already published them online,becouse he has been indirectly blackmailing her and telling her that he has her photograpes and that he will make her repent becouse she broke off with him when she came to know he was cheating on her...