Well, if you don't like circumstantial evidence, and you don't like eyewitness testimony, what WOULD cause you to condemn a man? Or are you just saying you oppose the use of the death penalty at all? Not taking any particular adversarial position on it myself, I just can't follow what you're thinking.
Physical evidence when collected properly is pretty hard to defend against. It's not complicated. I take the death penalty seriously. I support it. But when it is used, I want there to be no question whatsoever about the guilt of the man being put to death. The day we execute a man who is later found to be innocent will be a bad day for the death penalty in this country.