As murder scenes go it was a fairly cut and dry affair.

The victim lay dead where he had fallen. The prime suspect had fled the scene. And the murder weapon was easy to find: it was still sticking out of the King's heart where he lay in the New Forest.

But a little over 900 years ago the demise of Rufus the Red, King of the English was accepted as an unfortunate accident.

Since then every British schoolchild has been taught that King William II, son of The Conqueror, died in a hunting accident aged 40 on August 2, 1100, when his friend and companion that day Sir Walter Tirel (Tyrrel or Tyrrell) accidentally shot him through the heart. The arrow had been meant for a stag but bounced off a tree to where the king stood.

The King's body was then unceremoniously dumped on a cart by local peasants who took it all the way to Winchester Cathedral. Sir Walter wisely fled.

Certainly that's the story that has been readily accepted by most history books, despite a nagging feeling ever since that William's death owed more to foul play than poor archery.

For a modern day reader of the facts surrounding the death of the King the clues would have all pointed in one direction. The killing was deliberate, and the murderer was surely Tirel, the man who had fled the scene in haste and scarpered across the Channel to take refuge in France. This was hardly the action of an innocent man.

But appearances can be deceiving. And today, as it was 900 years ago, it is difficult to separate fact from fiction when it comes to solving one of Hampshire's greatest who-dunnit's: who murdered Rufus the Red?

While controversy has reigned over where William was killed - at The Rufus Stone, near Beaulieu or elsewhere in the New Forest? - who pulled the bow string has always been accepted to be Sir Walter Tirel himself. Indeed, there's even a pub named after him at The Rufus Stone.

And yet far from accepting he fired the fatal shot, Sir Walter never owned up to the deed in his lifetime, even claiming not to have even been with the King at the time.

Thus, off the record so to speak, the suspects have mounted up over the years.

Was it William's younger brother Henry, also out hunting that day and who seized the throne after the killing despite the fact his older sibling Robert, the true Duke of Normandy, had a better claim?

Was it Robert, recently returned from the Crusades and seeking the return of Normandy which he had rented' to William while he was away but now found his powerful brother was reluctant to hand back.

Or indeed how about Tirel himself? After all, until recently he had been a close ally of the rival French kingdom, owned castles and lands on the continent and had fled to the safe protection of King Philip I of France once William was dead.

Or was it, as writers at the time claimed, all a terrible hunting accident after all?

Now historical scholar and author Emma Mason has pointed the finger at another powerful candidate as the true murderer; none other than the King of France himself. In her new biography, William II, Rufus, the Red King, she argues that it was William's greatest rival Philip who had most to gain from the murder. In fact, had William not died when he did, just 13 years into his reign, Philip might have lost his throne all together.

To understand the facts behind the claim it's best to consider the state of England and indeed Western Europe at the time.

Far from being the relatively poor remote island kingdom that it had been before the Conquest, England at the end of the 11th Century was a true powerhouse. The uniting of the wealth of English taxation with the brutal military machine of the Normans had created a formidable force. This was after all a Europe where monarchs and their lords were expected to seek battle and conquest as a way of life. And William in his short time as King of England had proved himself an almost unstoppable force. By 1100 he had not only subdued rebellion in England and conquered Wales, but turned Scotland into a vassal state, brought Normandy under his control and captured the neighbouring county of Maine. With war in the French area of Vixen and ambitious plans to seize even more of what is modern day France, including the vast Aquataine itself, it is easy to see why Philip I might see his own throne at risk. He had good reason to feel unsafe, and his spies told him William was amassing a huge war chest and was preparing to cross to Normandy to be ready for battle.

It was Philip, then says Mason, or at least his son the Prince Louis (The Fat), who arranged for the death of William that summer's day in Hampshire.

So Sir Walter was innocent after all? Probably not. Although he was most likely in another part of the Forest when the blow was struck, it may have been one of Tirel's men who, standing with the King, had shot him. Sir Walter though had wisely decided discretion was the better part of valour and left the scene to avoid any sort of enquiry.

But did they really think they could get away with it? Quite probably, after all there had been two other recent royal deaths due to genuine hunting accidents in the New Forest. King William's older brother Richard had been mortally wounded when he struck a tree while riding there during the Conqueror's reign. And William's nephew Richard, grandson of William the Conqueror, had been killed as recently as May that year when he too had been struck by a stray arrow near Brockenhurst. No one could deny hunting was a dangerous pass time even for royalty. It also could provide good cover for murder.

And what of William's younger brother Henry? He did after all have the most to gain: the whole kingdom. Could he also have been involved? Perhaps, claims Mason, but most likely he knew nothing of the details of the plot but stood ready to make his move should William fall.

If Mason is right, then Philip calculated correctly that Henry I would be too pre-occupied in holding his new kingdom to consider war on France.

And Sir Walter? He remained holed up in his French estates but when he finally returned to England he was welcomed by Henry.

But why, if the murder suited everyone, did the death remain referred to as an accident for so long?

In short, claims Mason, because it also suited everyone to keep it that way. After all, chroniclers writing of the incident for many years to follow had to keep in mind the fact Henry or his heirs were sat on the throne. To claim they had come about it by murder might not have been good for the health. Such writers might just have met with their own unfortunate accident.

William II - Rufus the Red King by Emma Mason is published by Tempus, price £25. www.tempus-publishing.com