Moroni could have easily slaughtered the guards and released the prisoners. Mormon suggests that it is because Moroni was not bloodthirsty. No doubt this was true. Moroni may also have been under a code of war that accepted personal combat, but frowned on the slaughter of innocents. If the Lamanite guards had been met in the open, Moroni would have had no compunction about fighting them. Moroni’s hesitation was for the less honorable method of achieving his ends.