@_Confederacy_ Use a gas chamber
accept the request and once they are there you log and have a friend / alt proceed to bombard them with harming potions fired from dispensers above them. (this is an enclosed area)
I'm surprised nobody has thought of this.
It would be very quick leaving a very small amount of time to do anything. And lining the walls with obsidian would make escape something very hard to do.
Same with my idea >:)