The problem with the death penalty for rape is that many juries would not convict, even when they thought the perp was guilty, because they did not feel right about the death penalty for a case where the victim herself, though brutalized and assaulted, did not die. The Supreme Court outlawed the death penalty for rape in, I think, 1977, and victims groups were actually glad, because too many rapists were found not guilty by juries unwilling to affix the death penalty.
The solution, now that we have DNA to work with, is to put all of 'em down, and to select hanging juries.