When you have nothing on someone, but want them arrested and the book thrown at them, perhaps to barter information--"tell me, or go to jail;" or for reasons like, "stay quiet, or go to jail;" "lock him up until this blows over;" "make sure he doesn't talk, or that no one listens," etc.--you trump up a charge of "child porn."
Then they'll tell you about how these guys, along with child molesters, have yucky experiences in jail. A little fear never hurt controlling someone, right?
It's easy because you don't need a witness or victim whose story can be questioned or shown to be a lie.