Assassin's Creed Game Guide 3
It would've been possible to replay this and perform a better assassination, but avoiding the mental patients is pretty frustrating here.
If you wait until he comes up to the paitent closest to the door where the monks are, have your hidden blade selected, and wait until he starts off to the next paitent, you can do a tackle-kill (forget the technical term). Then you just have to get yourself out, which, really no matter what, is going to ba a challenge.
I waited so the man would get to the midle and then jumped on him, and well easy kill! (I played on PC)