Blackstone's formulation.
"better that ten guilty persons escape than that one innocent suffer"For a guilty man to go free is unfortunate, but for an innocent man to be punished is a tragic.
Innocents are still executed because the justice system is not perfect. Although DNA evidence has reduced the frequency of this happening, it still does occur. Until we have a legal system that can sentence individuals with complete certainty of their guilt, no punishment as irreversible as execution should be used.
"By 1999, thirteen death row inmates had been exonerated by independent investigations of the facts supporting their convictions, including revelation of their confessions were coerced, and DNA tests had identified other as the actual murderers."