Using DNA exonerations for capital rape-murders from 1982 through 1989 as a numerator, and a 407 member sample of the 2,235 capital sentences imposed during this period, this paper shows that 21.25 percent or around 479 of those were cases of capital rape-murder. Data supplied by the Innocence Project of Cardozo Law School and newly developed for this paper show that only two-thirds of those cases would be expected to yield usable DNA for analysis. Combining these figures and dividing the numerator by the resulting denominator, a minimum factually wrongful conviction rate for capital rape-murder in the 1980s emerges: 3.3 percent. The paper goes on to consider the likely ceiling accompanying this 3.3 percent floor, arriving at a slightly softer number of the maximum factual error rate of around 5 percent. To a great extent, those who believe that the criminal justice system rarely convicts the factually innocent and those who believe such miscarriages are widespread have generally talked past each other for want of any empirically justified factual innocence wrongful conviction rate. This paper attempts to remedy at least a part of this problem by establishing the first such empirically justified wrongful conviction rate ever for a significant universe of real world serious crimes: capital rape-murders in the 1980s. Appendix 1 and 2