This makes little sense to me. Why would anyone "go along" with this unless they are ALREADY blackmailed. But if they are already blackmailed to the point that they are willing to rape and murder children, why is there a need to "up" the blackmail?
As anon here notes, normal people have NO desire to do such things, which is why most blackmail must seemingly involve things that morally flawed people actually WANT to do and think they can get away with… embezzlement, sex with teenagers, but NOT rape and murder of children.