Yeah, David was Charlie. He had Multiple Personality Disorder.
The neighbor came out because he saw David acting weird outside, going in and out of the woods with a shovel, running around with a flashlight yelling "WHERE ARE YOU?", etc. The neighbor was concerned and wanted to see what was going on. David, not remembering his actions when his brain was in its "Charlie" personality, thinks the neighbor is Charlie and attacks him with a knife.
------------------------------------- Former username Kawada_Shogo