The death penalty is irreversible and so convicts receive an automatic appeal and most states have extremely strict standards for execution. What this means is that if anything is even remotely out of order, it's entirely possible to get the convictions overturned - even when the person in question is guilty. The Eastburn Family Murders [1] are a perfect example of this.
The murderer/rapist was initially convicted and sentenced to death. Effective defense was able to get his conviction thrown out. Normally this would mean you walk free, due to double jeopardy protections. But in this case the murderer was a military officer. Once DNA testing was refined, it was proven conclusively that he was indeed the murderer/rapist. So he was tried in the military court system, which is independent of the double jeopardy protections provided in the civilian court system, and convicted to death - again.
The point I make here is that many of those 190 probably are guilty, and I think this is generally not a bad thing. My main concern with the death penalty is an innocent man being put to death. But if the standard of conviction is sufficiently high that even a guilty man can walk free, at least on occasion, then that gives one some degree of assurance in the ability of an innocent man to prove his innocence.
[1] - https://en.wikipedia.org/wiki/Eastburn_family_murders