It was way back when Mike Johanns was governor. A mother and daughter of a murdered man had come to oppose the death penalty and came to the Board of Pardons* to beg for his killers life.
It didn't work and the quirk was soon forgotten about, mostly, even by me.
It may well be the case that women who have been wronged in this case are somewhat expected to be merciful towards those who killed their loved ones. If a movement of righteous avenging Fathers of murder victims opposed to the death penalty were to come about it may have more of an impact. It would have to be a movement too, as only one or two such fathers could simply be dismissed as unmen without any trouble at all.
(* The Board of Pardons consisting of the governor, secretary of state, and attorney general, is unique to Nebraska, created to prevent the horrors that would result from one person holding absolute power over mercy.)