I have to agree with Bug and P-man on this one. What is done is done. If you made a mistake fix it the best you can and move on. DNA IS now available, as is the knowledge of the inaccuracy of eyewitness, so the mistakes, which were rare to start with should now be much more so. There is no justification to endangering guards and other inmates by keeping men in prison for life, in paying for food, housing, clothing, and medication for maybe 60-70 years. Not only that, it is more cruel to keep a man in a cage his entire life than to kill him, especially just so someone that is indecisive can hedge their bets. You cant bring someone back, but the monument and compensation for the family are the right thing to do.
If you believe in the sanctity of life, up to and including not killing in self defense, I salute you, you are in fact right up there with Jesus, I will give you my front row seat any day.
For the rest of us, I can only think of ONE argument against the death penalty, and that is that SOMEONE has to execute the convict. The effect on that person must be incalculable, regardless of how great or small it may ultimately be. This is one reason I would let a family member, friend, person who had suffered something similar flip the switch if they would. They have the moral right by their loss, regardless of the process, the state does not, just the legal authority.