Advancement, of course. Listen carefully. Look deep within yourself, Clarice Starling. Go seek out Miss Mofet, an old patient of mine. M-o-f-e-t. Go now, I don't think Miggs could manage again quite so soon, even though he is crazy.
Look for severe childhood disturbances associated with violence. Our Billy wasn't born a criminal, Clarice. He was made one through years of systematic abuse. Billy hates his own identity, you see, and he thinks that makes him a transsexual. But his pathology is a thousand times more savage and more terrifying.