There are six categories for civilians. Arcane (wizards and scholars), Weaponry (any armed figure), Expensive (nobles or bankers), Tools (workers with spades, mops, picks etc), Consume (vendors with food and drink or folk consuming same), Perform (performers with musical instruments, puppets, snakes etc). There are sub categories but that is less important.
Guards can be armed, but often violence is not needed; cutting down non-violent suspects causes discontent. Sometimes ropes or chains or just an open hand are best. Lanterns and torches are useful for investigating. Ranged weapons can also be useful but you won't want more than one.
The game has a very strong narrative RPG-like element, driven by the plot cards (you will have a different selection in every game), plus a major plot, and also secret cards which come out during the game. Players are competing for glory, but cannot fight each other. They can however impede each other in various ways.
It's a fairly complex game but it is very engaging.