The Question All Death Penalty Supporters Need To Answer

It's a reasonable assumption that anyone who in any way supports the death penalty probably doesn't believe that executing a genuinely guilty heinous murderer is fundamentally wrong, so that's not the question. Rather, the question is this:

What is the highest rate of execution of innocent persons that could exist without making you cease supporting the death penalty?

This is a question that simply must be answered before a conversation about the death penalty can commence. But I rarely hear it asked. (The rate in question can be in just about any units: innocents per execution, innocent executions per capital crime committed, innocent executions per year, or per capita per year. Whatever.)