Lehi pursues them to keep the Lamanites moving in the desired direction – straight into Moroni. With the difficulties in communications, it is unlikely that Lehi knew that Moroni had taken Mulek. He would have faith that Moroni had accomplished his objective and moved according to the plan, but he would not have known this. Thus he moved cautiously, expecting that the Lamanites would meet Moroni’s army, and then the battle would trap the Lamanites between the two forces.