I only read Hannibal. But in that one he lays some groundwork for Lecter's backstory. It was far more compelling than what they did in the Hannibal Rising movie. And Hannibal has been nuts from the start. Essentially, his sister was eaten. There was a very specific reason Lecter was obsessed with Clarice and it makes sense in an insane manner. Clarice made him think of his sister. Years before meeting her Lecter had read something by some genius type about how we know time is moving forward. I'm paraphrasing heavily because it's been many years since I read the book, but the writer wrote something about a glass falling and breaking and remaining broken is how we know time is moving forward. Lecter had a theory that time could move backward and he would regularly push glasses off tables and stare at the shattered glass to see if it would reform and jump back up on the table. The only circumstance in which he would kill Clarice is if that glass jumped back on the table. Because to him that would mean he could slide his sister's mind/spirit into Clarice's body. I don't have any clue how a sane person comes up with that concept, but maybe Thomas Harris isn't sane.