The blame is placed on arbitrary, textual laws which sit in capital buildings. Some people think the death penalty is terrible, some think it's the only way. Get rid of the trash of the world. That's not the important thing. The important thing is that our legal and justice systems work and are free enough of corruption that they actually work and lessen the chance of people receiving the wrong punishment sentence.
Bribery is probably rampant in the courts, and most definitely lawyer manipulation is.
Our laws are constantly being edited in order to accommodate exceptions to the rule, which in turn produce precedents which are hard to counter in a court of law. A good percentage of the time, the right person is convicted. But with all the wheeling and dealing going on in the courts every day, the people who are guilty are getting off on exceptions to the rule, set by actual innocent people. Look, it doesn't matter if you're into religion or you're family to someone who got slain by a criminal who broke parole. What matters is that we find a system that minimizes wrongful deaths.