Hope descended into horror on Wednesday, as the US Supreme Court considered, and then rejected, a request from attorneys acting on behalf of Troy Davis to stay his execution. All the while, I am told, he was strapped to the gurney in the execution chamber waiting to die.

I am still in a state of cold disbelief; I cannot quite believe that this has happened - that one of the most advanced nations on earth has lapsed so easily into such unthinking barbarism. The trajectory of the Davis case through the state and federal courts is a complicated one, but one thing is clear: far from being 'guilty beyond a reasonable doubt', Troy Davis was probably innocent.

It is worth quoting directly from affidavits of some of the witnesses (seven out of nine) who recanted the testimony they gave in Troy Davis' original trial - in which he was convicted of murdering a police officer.

Kevin McQueen: 'The truth is that Troy never confessed to me or talked to me about the shooting of the police officer. I made up the confession from information I had heard on T.V. and from other inmates about the crimes ... I have now realised what I did to Troy so I have decided to tell the truth.'

Michael Cooper: 'I remember that [the police] asked a lot of questions and typed up a statement which they told me to sign. I did not read the statement before I signed. In fact, I have not seen it before today ... What is written in that statement is a lie.'

And yet, Troy Davis is now dead.

I was in Atlanta, Georgia last weekend and there was a strong public sentiment against Troy Davis' imminent execution. The fact that the state of Georgia proceeded with the execution, in spite of both the overwhelming evidence and the international campaign to stop it, is telling.

First, it is clear that the identity of the victim - a police officer who was trying to prevent an attack on a homeless man - shaped the contours of this case, creating an inexorable drive towards execution. If Davis had been guilty, this would perhaps have been understandable. But sacrificing the life of an innocent man is not, under any circumstances, a legitimate way to settle such a score - even if he was poor and black.

Second, the case speaks volumes about the institutional attitude of the relevant state bodies in Georgia - that they are loath to correct their own errors. The reluctance of government actors to admit their own mistakes is nothing new, but when it results in state-sanctioned murder something needs to change.

In response to the Davis case, the Reverend Al Sharpton has called for the reform of capital punishment in the thirty-four US states that continue to practise it. Crucially, he argues that nobody should ever be convicted of capital murder where there is no physical evidence linking him or her to the crime. This is something that everyone should endorse, regardless of your position on the death penalty.

The Davis case has rightly become a cause célèbre. What has been overlooked, however, is that the fate of Troy Davis is by no means unprecedented. Since the reintroduction of capital punishment in 1976, there have been numerous cases in which there was considerable doubt as to the guilt of those executed; indeed, the preponderance of evidence in these cases suggested that they were actually innocent.

There can be no restitution for individuals executed for crimes they did not commit. But let it be hoped that Troy Davis did not die in vain.