As Mormon was compiling and abridging this record, he may well have identified with Alma the Younger’s struggles. In Alma’s initial visit to the city of Ammonihah, he went all alone. He went without a bodyguard, without a companion, without other witnesses. While that strategy must have been extremely brave and sincerely impressive, it created problems because the people exclaimed, "Who is God that he will send only one witness against us?" (Alma 9:2). The people of Nephi generally observed the Hebrew legal requirement for two or three witnesses, "Wherefore, by the words of three, God hath said, I will establish my word" (2 Nephi 11:3).
At the end of his writings, Mormon may have had a similar or related thought, when he says that he stood as "an idle witness" against his people (Mormon 3:16). He too would stand alone. I believe that as Mormon went through this material, he was inclined to keep more of it when he identified personally with what was going on in the records, and he knew poignantly of the destruction that would come to his people as a result of wickedness. There are two places in the Book of Mormon where things became really, awfully wicked. One was here in Ammonihah, and the other was in Mormon’s own time. So, Mormon’s own personal interests and experiences may have been a factor in his motivations and inspiration for recording so many of the awful details in these chapters.