Statting up an assassin

[Phneri]

So my (APL 11ish) group has headed to a city for research and shopping, and I'm statting up a hit and run style bad guy whose intended to not offer much in the way of a direct challenge, but be incredibly annoying in terms of making the party look bad.

Idea is to have him look like various party members and be witnessed murdering (or leaving the scene) of various people the party have discussions with. Preferably altercations, of course.

I'm starting with the faceless stalker from bestiary 2 (aberrations fit well with the overall plot and I want to depart from doppelgangers). Clearly rogue fits this, but I wanted to see if anyone else had ideas to work with the concept?

[TarkXT]

Bards work just as well and with their spellcasting you can get away with using pretty much anything.

Alternatively just the base stalker works for this purpose. No need to add class levels.