Reminded me of "Psycho", and even more so the recent series "Bates Motel" which was suppose to be a "Psycho" prequel. A comment by our 16 yr. old central figure connects the three movies/series, "I'm a man now. I'm all grown up. I can take care of you now.", in reference to his now dominating his "single" mom. A sub-theme, behind the tragedies, is whether a psychopath is primarily the result of genetics or environment (of course some of each, but just looking at primary sources).
Disturbingly well acted; you will never trust a smiling courteous person again after seeing this. Background sound effects, and music were spot on appropriate.
Negatives are: Need a more creative title; ending could have used a bit more thought; research by the writers as to an unconscious person under water for some time is still using O2, and upon first consciousness will gulp in water which obviously is not good.