I start out thinking Gulliver Foyle's suggestion a bit too extreme, because some mistakes are likely to happen even if one is diligent and honest, and penalties too great might make prosecution too risky. On the other hand, the "eat your own dogfood" approach has some merit in that it brings home the realization of how extreme and irreversible the death penalty is. So I think if you could present it in the form "if you want a death penalty, here's the way it must be done," it would result in an end to the death penalty.
But I think there's a danger too, in this bizarre and skewed society, in which, if the penalty is so extreme, it would result instead in a system whereby, instead of instilling caution in prosecutors, it would insure that initial error is irreversible, and exoneration simply ignored or disallowed. We've already seen a couple of examples of this, in which execution was urged or even carried out on the grounds that the exonerated person had not met some time line or procedural rules.
In the mean time, I'd favor Chanakya's approach. For corruption or purposeful error, big penalties, for mere incompetence or failure of diligence, lesser perhaps, but at least dismissal with prejudice. There's an old English common law principle, that a dog is not vicious until proven otherwise. Every dog gets one bite. That's the bite.