And a little something for the other side:
'Cases involving innocent men condemned to death are not all that hard to find and are not as rare as the public might imagine.
An article in The Miami Herald on July 11, 1988, describes the case of 14 prisoners who were sentenced to death and later were found to be innocent.
An article in the Stanford Law Review in November 1987, reports an extensive nationwide study that found 349 such cases. The book, In Spite of Innocence, expands on the Stanford study and found that since 1900, there have been 416 documented cases of innocent Americans who have been convicted of potentially capital cases.
Unfortunately, once an innocent man has been convicted and sentenced to death, his chances of eventual exoneration are poor. Before the trial, the defendant does not have to prove anything. The burden of proof is on the state, which must prove the defendant guilty beyond a reasonable doubt.
However, after the defendant has been found guilty, the presumption of guilt shifts in favor of the state. Now the burden falls on the defendant to prove to the court that he is not guilty. And now it is no longer enough to raise a reasonable doubt--to overturn a conviction, the defendant must produce 'clear and convincing' proof of his innocence. This new evidence often must be presented within a limited time.
For the sake of argument, let's assume that there are some individuals who, in some sense, deserve to be executed. The real question that should be asked is: Do we really need the death penalty? As long as capital punishment remains a part of our penal system, innocent persons will continue to be executed. It is inevitable.'
http://www.abanet.org/irr/hr/innocent.html