Alma now faced a fourth challenge during the first year of assuming office as Chief Judge. Alma stood alone as the sole judge over Nehor’s case. Nehor had taken full advantage of the new freedom of belief provided under the law by Mosiah. Nehor must have felt confident in his legal position. It appears that he did not resist arrest, for there is no mention that he was bound. This, however, was likely a case of first impression—the legal issue being what to do about someone introducing priestcraft into the community and where to draw the line between "belief" and "action." Under the new reforms, a person could be punished for their actions, but not for what they believed.
Nehor defended himself. We are not told what arguments he made in his defense, but there were several issues he could have raised.
This left Alma faced with making a difficult legal decision. If Nehor were not convicted of a serious crime and was released back into the community, the people of the city of Gideon would feel that justice had not been served. The blood of an innocent man would cry out from the ground. In addition, Nehor would have felt emboldened, and where would that lead?
Alma was brilliant in how he decided the case. Notice that Nehor was not convicted of homicide. He was found guilty not only of priestcraft, but for enforcing priestcraft with a sword (Alma 1:12). Until very recently, priestcraft had been viewed as destructive in Nephite culture. However, as Nehor now saw it, exercising priestcraft was no longer a crime—to him it was simply expressing his beliefs. However, when Nehor tried to enforce his views with the sword, he took action and went beyond the simple expression of belief. Alma skillfully put those two facts together and essentially created a new composite crime—enforcing priestcraft with a sword. That was the crime for which Nehor was put to death. Alma did the right thing legally, politically, and religiously in pronouncing judgment against Nehor.
Alma’s decision also set legal precedent. Notice that dissidents continue in the first half of the book of Alma to argue and fight over the ideologies introduced by Nehor. However, they did not fight with swords.
Book of Mormon Central, "Why Did Nehor Suffer an ‘Ignominous’ Death?" KnoWhy 108 (May 26, 2016).