Humans are by nature imperfect. Mistakes undoubtedly are made in judging capital cases. If we conceed that people will make errors in judging capital cases it stands to reason that they will make errors in judging non-capital cases as well. If verdicts in these cases are wrong obviously many many other types of cases have been judged incorrectly. There is no such thing however as an unbiased computer program bereft of human input that can make 100% accurate judgements in all cases. Yet one does not hear of anti-death penalty folks railing against the injustice of people who have lost their cases in divorce court.
The criminal justice system is not perfect. This is not news to anyone. If an error can be made in a capital case, it can be made in a divorce court proceeding, or when someone is suing in small claims court for $100. Heck, I think Judge Judy is full of shit at least 20% of the time.
If the convicted person feels that an error has been made he should be able to appeal a verdict. Such is usually the case in capital punishment cases. How long did it take to put down an animal like John Wayne Gacy?? He was on death row for 14 years before he got what was coming to him. I won't lose sleep over the fact that he was able to avail himself of lawyers who defended him to the hilt & filed appeal after appeal to keep him alive. He got the full benefit of the system. He certainly enjoyed many more additional years lived than his victims. He denied them their right to exist yet he was afforded the benefit of the doubt, and lived at tax payers expense in prison for years before being eradicated.
There are some high profile cases of people having gone to jail for crimes they did not do. In particular cases come to light that are solved by D.N.A. testing. They are not the rule though. They are the exception. Serial killers are exceptional. They do things so beyond the pale of humanity, so sickening, so absolutely despicable that they don't deserve to live. Some want to get rid of the death penalty because of these exceptional cases. I say keep it because of exceptional cases. The Green River killer'll probably get life in prison with no hope of parole in exchange for telling investigators where he buried some of the bodies of his victims. Truth is that bastard should fry in the electric chair. If anyone has it coming he does. The evidence against him is overwhelming, yet we should allow him to live out the rest of his life because D.N.A. exonerated a guy in jail for a rape? The two situations are different.