I've long been in favor of the death penalty for murderers, and that isn't changing. If a person commits murder, justice may often be best served by executing that person.
What is changing is my confidence in the ability of our government to accurately determine guilt and innocence. I don't trust our government in general. Like a negative King Midas, everything the government touches turns into a self-interested bureaucratic nightmare. I don't want the government running our economy, our sex lives, our schools, our media, or our gun stores. I believe our government (federal and state) should do as little as possible while effectively protecting our God-given liberty.
However, the government is the best known institution for punishing violent criminals and it needs to be the central actor in the administration of justice. There is no real substitute for government action when it comes to punishing violent criminals, so we're stuck with its imperfect behavior which is often tainted by laziness, corruption, and politics. Prosecutors, police, and judges are often good people who try to do the best they can... but not sometimes they aren't, and it's often very hard to tell. Putting an innocent person in prison is bad enough, but at least you can release the person later if you discover that you've made a mistake. But dead is dead. I have no doubt that our justice system has executed innocent people.
Consider the case of Anthony Porter. He was 48 hours from being executed when he was granted a stay, and he was later exonerated. It is important to note in this case that his stay of execution was not granted because there was any doubt about his guilt.
In 1995 Porter was tested to have an IQ of 51, meaning that he may have been moderately retarded. A new appeal was filed on the grounds that Porter was incapable of understanding his punishment. Forty-eight hours before he was scheduled to be executed in 1998, another stay was granted.
While this appeal was pending, a man named Alstory Simon confessed to the crime of which Porter had been convicted. This man was not in prison, did not know Porter, and had no incentive to confess falsely.
On January 29, 1999, Inez Jackson, the estranged wife of Alstory Simon, came forward and said that she had been with Simon when he killed Hilliard in retaliation for "skimming money from drug deals." She also confirmed that she had never met or seen Porter. Her nephew, whose apartment Simon fled to after the shooting, came forward to corroborate her story. Four days later, on February 3, Simon himself confessed to the crime on videotape. Protess and the students came forward with the information. Two days later, Porter was released from prison, and the charges against him were dropped the next month. Simon was formally charged with the murders. In September of 1999, Alstory Simon pleaded guilty to two counts of second degree murder and was sentenced to 37½ years in prison.
Anthony Porter would have been executed if he hadn't been granted a stay because of his mental retardation. No one in the legal system doubted his guilt. The system failed. I doubt Porter's situation was unique. With apologies to the majority of police, prosecutors, and judges who do good work, I am no longer confident that our justice system as a whole should be entrusted with the power to put people to death.