Whether it is lawful to kill the innocent?

Objections

Objection 1 : It would seem that in some cases it is lawful to kill the innocent. The fear of God is never manifested by sin, since on the contrary "the fear of the Lord driveth out sin" (Ecclus. 1:27). Now Abraham was commended in that he feared the Lord, since he was willing to slay his innocent son. Therefore one may, without sin, kill an innocent person.
Objection 2 : Further, among those sins that are committed against one's neighbor, the more grievous seem to be those whereby a more grievous injury is inflicted on the person sinned against. Now to be killed is a greater injury to a sinful than to an innocent person, because the latter, by death, passes forthwith from the unhappiness of this life to the glory of heaven. Since then it is lawful in certain cases to kill a sinful man, much more is it lawful to slay an innocent or a righteous person.
Objection 3 : Further, what is done in keeping with the order of justice is not a sin. But sometimes a man is forced, according to the order of justice, to slay an innocent person: for instance, when a judge, who is bound to judge according to the evidence, condemns to death a man whom he knows to be innocent but who is convicted by false witnesses; and again the executioner, who in obedience to the judge puts to death the man who has been unjustly sentenced.