MKX said:
Quite a lot of the Arbites and Inquisitions power is backed up by judicious or excessive force, blackmail, coercion and general bastardry, as required.
Never excessive force. The thing about excessive force, like torture, is often that it makes people confess whether or not they're guilty... and that just won't do.
Beyond that, as the Adeptus Arbites are fond of saying: "To be just, our Law must be cruel". But at least it's cruel to everyone... it's just fairer that way.