https://youtu.be/HnHrNpwMnTs
Loving an enemy of this kind means to will his highest good, and that is to do our best to ensure he achieves the beatific vision, and this requires his repentance. This does not mean we preserve his mortal life but use this opportunity to bring about the deepest contrition possible.
For this circumstance, what would elicit contrite repentance more than an impending end of life? Anyone who cowers at the suggestion is not brave. Courage and solemn justice are difficult virtues when a man has unjustly taken the life of an innocent, and I do not envy the responsibility of the agent of the state, but it must be done.