Jaqen changed his face in front of Arya and the guy with this exact appearance was the one who killed Pate.The real Pate was the young Citadel student killed in the prologue. By the end of the book he's been replaced by the Faceless Man - presumably Jaqen H'ghar - who killed him.At the end of the 4th Book, who is Pate? Why was he saved as the last lines of the 4th book?
I get that the guy at the end is the killer at the beginning, but how did you get that he's a Faceless Man, more specificly Jaqen H'ghar? (no book 5 spoilers please)