Verse 12 notes that “this is the first time that priestcraft has been introduced among this people.” That statement must refer to the people under Nephite government. We do not know if it existed in Zarahemla prior to the time that the Nephites arrived, but the undercurrents we see in Zarahemla suggest that it was.
Alma is defining priestcraft as teaching that the priests should be paid and not work with their hands. The implicit indictment is that this is also the introduction of a significant form of social inequality.
The second crime is attempting to enforce his religious beliefs through force, which resulted in Gideon’s death. There was no apparent controversy over whether or not the man had slain Gideon. Therefore, the law applied, and, as Alma declares: “thou art condemned to die, according to the law which has been given us by Mosiah, our last king.”