They are more interested in gathering evidence than fighting.
The Goomba: The weakest of the Agent types and typically the first of the Forces of Justice you will encounter.
Failed a Spot Check: The Pathetic Investigators/Agents can walk past piles of corpses and stolen loot without noticing them.
Thankfully your Genius has no such restrictions, since they can execute their own mooks anyway. However, most minions will ignore disguised agents, and even un-disguised agents if you forget to tag them. Even when in disguise their body language screams "I'm being suspicious!", letting a discerning player pick them out from a crowd.
Highly Visible Ninja: Zig-zagged in the second game.
Determinator: Seriously, the lengths of time that some of these guys will spend stood at a door to try and force it open is really quite something, particularly the Pathetic ones who are also extremely bad at it.
Poor Investigators tend to steal gold if they get into your strongroom while Good and Exceptional ones will try to take your loot as well.
Bandit Mook: Any Investigators that are not Pathetic will steal stuff if they get the opportunity.