....It is cases like Skinner's that ended my lifelong support for the death penalty. Any system driven by the decisions of human beings will produce mistakes. This is true even when everyone — judges, prosecutors and defense attorneys — is acting in good faith and working as hard as he or she can to get it right.

Tim Cole is only a recent example of the frailties in our criminal justice system. Several years ago, this newspaper argued persuasively that Ruben Cantu, a defendant I prosecuted who was put to death in 1993, may well have been innocent. Twenty years after Cantu's trial, my star witness recanted his trial testimony. Many people consider his recantation credible because he had nothing to gain by reversing his position except a whole lot of trouble.

That case brought home to me, in a way that nothing else could have, that the system we trust to determine who may live and who must die simply doesn't work in all cases. Other investigative stories have revealed that Texans Carlos DeLuna, who was executed in 1989, and Cameron Todd Willingham, executed in 2004, were almost certainly innocent.

Since 1973, 139 people in 26 states have been released from death row based on evidence of their innocence. Eleven of them were in Texas. Many of these people were freed because of DNA evidence. But DNA testing works only if we use it.

Read the whole commentary.