I searched it and couldn't find a satisfactory answer. Were there some sort of police or any kind of law enforcement organisation in the late middle ages? If yes, how could an officer tell when someone wasn't lying, a person could say someone killed another person only to get him arrested because they didn't get along?
You might want to take a look at this collection of some responses to similar posts, courtesy of /u/Searocksandtrees. There's also this answer by /u/cazador5 on England specifically.