The word 'murder' derives from the word 'murdrum.' Murdrum was a fine imposed by the first Norman king of England, Guillaume I, shortly after the conquest of 1066, and it was designed to protect the Normans who had come to England with him. If a Norman was found killed and the killer was not known, the murdrum fine was levied on the inhabitants of the entire area in which the body was found. The murdrum fine did not apply to English corpses, however.
Why would a law like this be needed? Presumably because a lot of Normans were turning up dead in mysterious circumstances. Many would have been victims of the people the Normans called the 'Silvatici' – the men of the woods, who were known to the English as 'green men'. The Silvatici was an underground resistance movement comparable to the French Resistance or the Viet Cong, and it flourished for a decade after the Conquest. It was mass resistance from the Silvatici that led to the Harrying of the North in 1069 – the land was stripped bare to leave them no hiding places – and to numerous other risings and rebellions which left a lot of Normans dead and made Guillaume's throne less secure than we might now assume. In fen, forest and field, it seems that a substantial proportion of the English population were prepared to resist their new masters.
Some of them remain legends to this day. On the fen island of Ely, an English landowner named Hereward resisted the Normans for years, building up an army of rebels, calling for assistance from the Danish king and, when Guillaume personally intervened in order to try and crush his rebellion, frustrating the king for years with tactics including the sacking of abbeys, the destruction of causeways and even the burning of the fens themselves. Over on the Welsh borders, an outlaw known as Eadric the Wild (or Eadric Silvaticus) refused to submit to the conqueror, and raised a rebel army which burned down Shrewsbury.
There would have been many more such rebels, forgotten now, who tried to hold back the tide of history. What do we remember of them today? Perhaps the English archetype of the outlaw in the greenwood, of whom Robin Hood is the best-known exemplar, began in the 1060s, with the rise of the rebels in the forests, fighting for their land. And perhaps we still see the green men in, of all places, our old Norman churches. It could be that those carved stone faces peering out from their haloes of leaves are more politically charged than we think.