Okay.
I disagree.
Mistakes happen. Policemen accidentally shoot innocent people. When it's not an accident, they are investigated and, if warranted, indicted, tried, and punished (if found guilty). Doctors accidentally kill people all the time...albeit, in many cases, in an attempt to save an already dying person. When it's not an accident, they are investigated and, if warranted, indicted, tried, and punished.
Executions, on the other hand, usually only occur after years and years of appeals and opportunities for the truth to come out. If, after all that, it doesn't, I'm more inclined to believe the truth was willfully and intentionally withheld by someone -- and that warrants an investigation and holding someone responsible.