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As a practical matter, I personally believe it is almost impossible to implement a state sanctioned death penalty without executing innocent people. Moreover, life and death decisions are handed to people with political power which automatically corrupts their judgment.
I actually can sympathize with some of the positive cases for the death penalty. It has a strong theoretical appeal but I find it impossible to support practically when I think through the implications of any implementation.
I do think it's literally impossible to have a death penalty without killing innocents. If you look at the stream of criminal convictions that get reversed by appellate courts on a daily basis, combined with all the exonerations handed down to deathrow defendants, it is clear a guarantee of guilt is impossible.
And bear in mind, that reversal of a conviction is usually only possible if there was a trial. Those who enter guilty pleas are often exempt. And 90%+ of defendants enter guilty pleas for a host of reasons. I think Trump's NY judge even commented recently that Cohen entry of a guilty plea wasn't evidence of his guilt (i.e. you might plead guilty and be innocent).
Having spent a lot of time in the justice system, it's clear criminal trial courts don't have the resources to ensure fair verdicts regularly, and don't have high-quality staff to run them.
Japan and South Korea have the death penalty.