It takes so long because they have constitutional rights to appeal. Getting someone executed is a very long legal process. Working in a law firm I can tell you that some civil cases will require what would amount 15-20+ large trash bags of paper work. That is just one case, with no appeals. Capital cases average 4x the paperwork than a non capital case. Imagine writing 60-80+ large trash bags worth of documents... that alone could take twenty years! I think that the slow process has to be protected. Even with the current system there are reports of innocent people being found guilty and sentenced to death. If the time between conviction and execution were any shorter, more innocent people would be killed.