Today we have DNA, security camera's, text-messages,... All ways of proving someone's guilt but what forms of proof were there in the medieval period en extending on that, in a period where the nobility held real power how could a king arrest one of them say when they conspired against him. What proof would he have so that the other nobles wouldn't revolt or so, or would it be very common for a king to arrest opponents as he didn't need any proof and there wouldn't be much of a reaction either?