There could also be a module you can add called, "Captive Random Events," where the captive may break out of your cuffs (Can happen) or, is able to open the door of the vehicle it is in, and jump out. Or he can start to run away without even taking off his cuffs. It could really lead to some fun missions.
EDIT: Maybe if people wanted to, there could also be a module that says, "Only MP can arrest" this is pretty self explanatory, it makes the MPs the only people who can arrest citizens or enemies, or whoever. This of course means, you need to add MPs to the game ;).