The problem is if there has been a miscarriage of justice. In the UK, two men in the 1950s, in separate cases were executed and later found to be innocent. Just last year a children's nurse was found guilty of murdering babies in her care. There are now serious doubts about her guilt. There is no death penalty in the UK now. If there were maybe she would have been executed by now. You can't bring dead people back. Their family and friends go through the same, or worse heartache than those that they were wrongly accused of murdering. Worse, because they were innocent.