Keys?

[PZ]

I did an assassination contract this morning in which I was to find and kill a messenger who had a note informing of a bounty hunter (with my name on his knives).  All went normally, but when I killed the bounty hunter and looted his body, a single key was one of the objects I took from the body.  I've no idea what that key is for yet.

[spaceboy]

ever find out?  This hasn't happened to me and I completed the story missions, but not all the side missions.

[PZ]

Nope - never did discover anything.  Maybe something to do with the Auditore vault or one of the un-lockables?