Canon 1090 of the Roman Catholic Church is called the impediment of conjugicide.
This impediment technically applies to two parties who with a view to entering marriage kill their spouses in order to establish a marriage bond.
This impediment is also called the impediment of crime. The scope of this crime of conjugicide has been narrowed in the 1983 code than what was formerly the legislation in the 1917 Code.
In the former code, there were four factis species of this crime but in the new Code the crime of conjugicide has to be interpreted strictly to entail a real killing of one’s spouse with the intention to marry the deceased’s spouse. The new interpretation of the law entails three situations:
1) The murder of one’s own spouse.
2) The murder of the spouse of one whom the murderer intends to enter marriage with;
3) The murder of a spouse with mutual cooperation. It also extends to a mutual decision and execution of the murder of both spouses in order that the two criminals are free to enter marriage as a result of the dissolution of their previous bond by the death of their former spouses.
This impediment of crime is of natural law origin and the dispensation from the impediment is reserved to the Roman Pontiff (cf. Paul VI, M.P. De episcoporum muneribus 1X, 13 of 15th June 1966 (AAS 58), 471).
The reason for the impediment is that people who commit a crime especially should not be condoned to benefit from their act whatsoever, not to think of benefiting from the sacrament of the Church. It is also meant to safeguard public order, preserve the sanctity of marriage which dissolves naturally by natural death and the impediment also serves to protect the integrity of family and the good of the children.
Another impediment to marriage is consanguinity in all degrees of the direct line, whether ascending and descending, legitimate or natural (cf. Can. 1091 par.1). This impediment of consanguinity also extends to relationship any blood in the collateral line up to the fourth degree inclusive (cf. Can. 1091 par.2). The degree of consanguinity is a natural law impediment that is common in all cultures, religions and human societies.