Moroni has the authority to execute traitors and exercises it here, observing the formalities of imprisonment, trial, and the option to serve in the army, presumably guaranteed by an oath or covenant. The king-men’s treasonous activities had endangered the entire nation, not only because of their dissent but because of their open collusion with the Lamanites (Alma 61:8). Had they been allowed to live they would have certainly attempted a similar rebellion again.