Mormon is unable to assist the “widows and daughters” in Sherrizah because his army cannot break through a Lamanite army that stands between them and Sherrizah. He clearly would assist if he could, but he cannot. How does Mormon know what happened if he can’t get there? Mormon’s army cannot get there, but there would be ample opportunity for small groups to move through the land and scout the area. Certainly any general would have his spies to know the movements of the enemy, and those spies would be in a position to know what happened, and to return and report.