In Moroni 9:17, Moroni quotes Mormon as stating that "as many [of the Nephites] as have fled to the army of Aaron have fallen victims to their awful brutality." Apparently because these people were traitors in the thick of battle rather than peacetime "dissenters" (Moroni 9:24) the Lamanites had very little respect for them and treated them with "awful brutality." [Alan C. Miner, Personal Notes]
“The Army of Aaron”
In the ninth chapter of the book of Moroni, Mormon's epistle to his son Moroni speaks about the circumstances of the war between the Nephite armies and the Lamanite armies. Mormon mentions a Lamanite commander by the name of "Aaron" (Moroni 9:17). This might be a chronological clue as to the time period in which Mormon wrote his epistle. According to Mormon 2:9, the Lamanites in the year 330 A.S. (45 years previous according to my chronology) had a king and his name was "Aaron." At that time he commanded an army of 44,000 against Mormon's 42,000 and Mormon's army beat the Lamanites. However, Mormon was only 20 years of age at that time and now he would have been 65 years old. Therefore, depending on the age and longevity of the Lamanite king Aaron mentioned in Mormon 2:9, the "Aaron" in Moroni 9:17 could possibly have been the same person. [Alan C. Miner, Personal Notes] [See the commentary on Moroni 8-9 (Chronology)]