SPOILER ALERT .... DON'T READ THIS COMMENT UNTIL YOU FINISHED WATCHING THE WHOLE MOVIE
this movie is one of the best .... David was a nice person and tried to help the family in anyway he can ... he protected them and helped them ... but later we realised that David had been gone through some kijd of experiment that messes up with his head and if he feel his true identity is going to be revealed.. he will gone berserk and kill anyone who might find out!! .... he killed the family while he loved them ... because he couldn't control his behavior once he feel threatened.... when the military came to their house to kill him ... he didnt kill the mother at first ... but after mother got suspected and told him did you really knew my son in srmy ? ... he couldn't stop it and killed the mother ... he had to kill them and the saddest thing was the scene when he killed the last army man in the Halloween theme .... he put the gun down near him because he wanted the girl and his brother to kill him .... he could easily kill them all but tried to stop himself and helped them to kill him before he kill them .... after the boy stroke him with the knife (that David himself gave it to him) David tried to speak with the boy and told him "you did the best thing and don'tlet it bother you" .... sad it all began when the girl suspected him and tried to know who is this guy.... otherwise he would never do these things ... I liked his character until the very end ..... a very good movie ... also a good soundtrack .... damn I enjoyed it all and watched it nonstop till the end