3. Grave breaches of Scheduled Conventions.

(1) Any person, whatever his nationality, who, whether in or outside the State, commits, or aids, abets or procures the commission by any other person of, any such grave breach of any of the Scheduled Conventions as is referred to in the following Articles respectively of those Conventions, that is to say :
...
shall be guilty of an offence and on conviction on indictment thereof :

(i) in the case of such a grave breach as aforesaid involving the wilful killing of a person protected by the Convention in question, shall be sentenced to death or to penal servitude for life or any less term ;