I agree with you. Circumstantial evidence should rule out the death penalty. Even witness testimony is questionable at times. I don't pretend to have a set in stone guideline. I think circumstances dictate the sentence.
I think we, as a society, need to ask ourselves are we willing to accept an imperfect system of justice dealing out ultimate justice from which there is no do-overs? If the answer is yes, what percent accuracy would we be willing to accept? Reliability of 100% is just not realistic. Interesting survey and results.