Alma 1:11 - 1:15

Alma 1:11 And it came to pass that he stood before Alma and pled for himself with much boldness.

Nehor was brought before Alma to be judged for the murder of Gideon. However, in spite of the seriousness of the charge against him, he was very confident about his persuasive capabilities and maybe thought he could get away with it.
[Nehor probably was making the charge that Gideon was trying to keep him from preaching his doctrines and that he had the right to preach and use force if necessary.]

Alma 1:12 But Alma said unto him: Behold, this is the first time that priestcraft has been introduced among this people. And behold, thou art not only guilty of priestcraft, but hast endeavored to enforce it by the sword; and were priestcraft to be enforced among this people it would prove their entire destruction.

The charge that alarmed Alma even more than the murder was Nehor wanting to introduce what Alma calls “priestcraft.” Priestcraft which means the support of the clergy with money or taxes so they would not have to work for a living. And even more insidious to Alma was Nehor wanting to enforce priestcraft by some sort of laws or even force. This, Alma said, would literally destroy the Nephites civilization.
[I think that looking over the history of Europe and the Catholic Church after the death of Christ can certainly illustrate this point. None of the civilization or empires that forced the people to have a particular belief system exists today. Traditions and cultures sometimes survive, but the institution of beliefs by force has only lead to wars between countries, revolution and even more destructive Civil Wars where family fought against family and relatives against relatives. This fact was well understood by the framers of the US Constitution and they specifically stated that Church and State should be separated and that religion could not be forced on anyone either by forced attendance or the payment of taxes to support those who work in the church.]

Alma 1:13 And thou hast shed the blood of a righteous man, yea, a man who has done much good among this people; and were we to spare thee his blood would come upon us for vengeance.

After hearing the facts of the case, Alma judged Nehor that he had killed an good man for no good reason. Further, if the crime was ignored, then the judgment of God would come upon the people for not prosecuting this crime.

Alma 1:14 Therefore thou art condemned to die, according to the law which has been given us by Mosiah, our last king; and it has been acknowledged by this people; therefore this people must abide by the law.

Alma said because of Nehor being found guilty of murder, he was condemned to death as it was the law of the Nephites which had been agreed upon by the people during Mosiah’s reign.

Alma 1:15 And it came to pass that they took him; and his name was Nehor; and they carried him upon the top of the hill Manti, and there he was caused, or rather did acknowledge, between the heavens and the earth, that what he had taught to the people was contrary to the word of God; and there he suffered an ignominious death.

Nehor was then taken to the top of the hill Manti and there allowed to confess his trying to mislead the people to God and the people and to confess that he knowingly murder Gideon for opposing him. He was then executed suffering an “ignominious” death.
[The form of death was not mentioned but it was called ignominious means “deserving or causing public disgrace or shame.” In other words, Nehor died in shame instead of the noble death of a good person in the normal course of life. It is interesting too, that Nehor knew what he was doing was wrong in that when he was up against the real truth of his actions that he freely confessed that he knew he was a liar and a fraud. This is a death bed confession so I don't know how effective it was.]