Capturing an enemy and holding them for ransom, in the middle ages, wasn't necessarily a crime. However, kidnapping a fellow crusader was not ok, since the pope has said that all the crusaders were supposed to treat each other well (by not capturing their lands and goods while they were off fighting, or kidnapping them and holding them for ransom), and also, there's a difference between holding a fellow noble for ransom and kidnapping the king of England. To be truthful, as far as medieval crimes go, this one isn't very criminal -- just sort of dumb, and tacky, but it gives a chance to discuss the rehabilitation of Richard's reputation (he wasn't a horrible king! he was ok!) and the importance of historical fiction.