Code of Canon Law - The Marriage Sacrament: Specific Diriment Impediments
Can. 1090 §1. Anyone who with a view to entering marriage with a certain person has brought about the death of that person’s spouse or of one’s own spouse invalidly attempts this marriage.§2. Those who have brought about the death of a spouse by mutual physical or moral cooperation also invalidly attempt a marriage together.
There is a distinction to be observed and recognized when a 'widower' has participated in or caused directly the death of their spouse -if such is the case then any marriage attempted would be invalid regardless any confession and or ceremony...
The people who are in favor of Schiavo and his longterm mistress getting married in the Catholic Church are the same ones who feel sorry for the Menendez brothers because they are orphans.