Reread the prologue to Feast. The Alchemist is deadon with Arya's description of the 2nd Jaqen. Its speculation, but pretty solid.
Yep. The fact that Pate shows up to talk to Sam later in the book after he already died in the prologue is proof that the person who kills him is a Faceless Man. The fact the description of the person who kills Pate matches Arya's description of Jaqen after he changes his face in ACOK makes him Jaqen.