Anyone happen to know how to alter whether or not an actor is capable of witnessing crimes? I'm not having any luck myself finding what would affect that.

I think if you remove them from the "XXXXXX crime faction" it might work. (Where XXXXXX is the hold they reside in.)

Actors can always witness crimes - removing the crime faction will instead make them warn the player / become hostile if they witness a crime. At least, that's according to the http://www.creationkit.com/Crime.

I don't think that's it. No animal has a "Crime" faction, but it's a well known issue that many animals can witness crimes.

Right. But why / how they witness crimes is still unknown. Likely has something to do with factions in general / the fact that all creatures are technically Actors now.