The last sighting of Beck was by one of the survivors, who saw him slumped under a tree with his head to one side, some time before the end of the battle; they couldn't be sure that he wasn't already dead at that point.
The last sighting of Beck was by one of the survivors. The survivors saw. Him slumped under a tree with his head to one side before the end of the battle. One side was some time. He wasn't already dead at that point. They couldn't be sure this.