Well, not only is the death penalty irretrievably broken, it is inherently broken. Four decades after the Furman decision, this is as clear as ever. Had the death penalty been a product, it would have been judged as shoddy, defective and unreliable.
At bottom, the primary cause for false convictions is the questionable quality of the evidence habitually used in criminal prosecutions. Poor evidence can be produced even when all actors follow procedures diligently and conscientiously.