Amnesty International's interest in the Kenny Richey case has been twofold - in the incarceration of an apparently innocent man but also in a striking example of the problems inherent in the death penalty.

As we finally see a positive outcome to the former, we should take a moment to consider the problem of the latter: that some governments still consider killing their citizens to be part of their legitimate duties.

Amnesty is opposed to the death penalty in principle, as a violation both of the right to life and the right to be free from cruel and inhumane treatment.

Yet there are also strong practical reasons why it is time to consign the death penalty to the same scrapheap as the stocks, branding and convict ships to Botany Bay.

Taking a life, the ultimate sanction, has no place in any fallible justice system, which is any system run by human beings. In Kenny Richey's case, prosecution lawyers tried successfully to argue for execution without all the evidence being heard in court.

It is so much worse in countries such as Saudi Arabia, where a confession extracted under torture can be sufficient "evidence" on which to convict.

Here in the UK, it is now accepted that the Guildford Four and the Birmingham Six were victims of a biased judicial system. They would likely have been executed had the option still been available.

Even if we could be certain of guilt in every case, researchers looking for evidence that the death penalty acts as a deterrent have been unable to find any. In fact, the great majority of murders are crimes of passion committed in the heat of the moment and murder rates are higher in US states which have the death penalty than in those which don't.

The death penalty is not even cost effective, as any credible appeals system means that a death penalty sentence costs more than life imprisonment.

A criminal justice system should dispense dispassionate justice rather than revenge or retribution. Proponents of the death penalty for murder cases often use the "eye for an eye" argument, but seldom suggest that torturers should be tortured or that rapists should be raped.

Attempts to find a "humane" method of execution are tying the US legal system in knots as shooting, hanging, the electric chair and lethal injection are each shown to bring their own version of mental and physical torment.

But let us end on a hopeful note. Countries which still execute are in a small and shrinking minority (only 25 countries did so in 2006, about one in eight). If Rwanda, with its recent traumatic past, can give up the habit then anyone can.

John Watson is Amnesty International's Scottish Programme Director