Forget the insanity defense for now, that's a different issue. I am actually arguing against some higher standard of evidence for the death penalty.
The statement was that we should only execute people based on "ironclad" evidence. That's a noble idea in theory. I'm just saying this higher legal standard is impossible to attain. You can find a way to question the veracity of any evidence that exists. Thats why our standard is "beyond REASONABLE doubt", and there is no higher standard. While you can question the veracity of the evidence, are those questions reasonable?
Even in the Clancy case, her attorney just filed a motion for an acquittal, claiming the evidence is all based on speculation. No one saw her commit the murders. There is a ton of evidence that she was there, and no one else was there, and she sort of confessed at the hospital. That was enough for a jury to find beyond reasonable doubt, but it certainly is not "ironclad".
Plus, for the death penalty, you first must prove murder beyond reasonable doubt, and then, in a separate trial, prove at least one aggravating circumstance beyond reasonable doubt. And even then, the jury must weigh the aggravating circumstances against mitigating factors.
And with all of that, we have still executed innocent people.
How would an "ironclad evidence" rule even work? After finding someone guilty beyond reasonable doubt, would the jury then have to decide if the evidence is "ironclad" enough to qualify for the death penalty?