In rendering his verdict Alma explained the responsibility of the people to execute anyone who has deliberately shed innocent blood. In modern times there are a number of states and sometimes whole nations who prohibit capital punishment. These nations are violating a strict commandment of God.
Here is the way the Lord gave this divine law to protect human life right after the Great Flood. The Lord said: "At the hand of every man's brother will I require the life of man. Whoso sheddeth man's blood, by man shall his blood be shed."1 Here is the way the Lord gave this commandment to Moses: "But if any man hate his neighbor, and lie in wait for him, and rise up against him, and smite him mortally that he die, and fleeth into one of these cities [of refuge]; then the elders of his city shall send and fetch him ... that he may die. Thine eye shall not pity him, but thou shalt put away the guilt of innocent blood from Israel, that it may go well with you."2
And here is the way the Lord said it in modern times: "And now, behold, I speak unto the Church. Thou shalt not kill; and he that kills shall not have forgiveness in this world, nor in the world to come. And again, I say, thou shalt not kill; but he that killeth shall die."3
Some people are opposed to capital punishment because they say that people should not kill and neither should the state kill. But the Lord apparently feels that when society does not take the life of a murderer in accordance with God's divine command it makes the life of the criminal more sacred than the life of the victim. To keep human life sacred, murderers are to be dispatched back to the spirit world. If society fails to do this, then her judges become parties to the crime.
This is what Alma was saying. If the members of the Church had not seized Nehor after seeing him kill Gideon, and if Alma had refused to sentence Nehor to die, both Alma and the members of the Church would have been under condemnation of the Lord.