Murdrum was introduced into English law by the Danes. Being the killing of a man in a secret manner, it is distinguished from simple homicide. In the Laws of Canute an unknown man who was killed was presumed to be a Dane, and the vill was compelled to pay 40 marks for his death. After the Norman conquest the law was revived in respect of the Norman aristocracy. It was abolished in the reign of Edward III . Richard I of England exempted the Knights Templar from being charged with murdrum and Latrocinium amongst other privileges.

http://www.essentialnormanconquest.com/encyclopedia/murdrum.htm