Hannibal Lector did not kill Benjamin Raspail. According to Lector it was "A fledgling killer's first effort at transformation". See reference from the script: You wanted me to find him.
His real name is Benjamin Raspail, a former patient of mine,
whose romantic attachments ran to, shall we say, the exotic.
I did not kill him, merely tucked him away very much as I found him,
after he'd missed three appointments.
- If you didn't kill him, then who did, sir? - Who can say? Best thing for him, really.
His therapy was going nowhere.
His dress, make-up...
- Raspail was a transvestite? - In life? Oh, no.
Garden-variety manic-depressive. Tedious, very tedious.
I now just think of him as a kind of experiment.
A fledgling killer's first effort at transformation.
Movies vs books[]
It depends which continuity you follow. In the novel Silence of the Lambs, Raspail is definitely a victim of Lecter’s, his ninth and final victim in the Baltimore series. In Hannibal, Starling again talks about Raspail being a victim, as his sweetbreads were served to his fellow musicians. Now in the movies, it’s more complicated. In Lambs, Raspail is a victim of Buffalo Bill. In Hannibal the movie, Raspail is now a victim of Lecter, with the details of the crime lifted from the book. In the movie Red Dragon, an incompetent musician (not named but based on Raspail from the book) is fed to his fellow musicians.