Spoilers 'Do you know, or do you not know?'
Was he human or was he an alien? I think he was an alien that entered Robert's body. I think Robert died partially when tried committing suicide that day. I think he was an Alien because he was way smarter than Humans at certain things like being able to communicate with the dog, and helping people realize stuff about life. I don't know, he just came off too intelligent to be from this planet. I know that the Sheriff said that Robert was a genius, so I guess you can say it is Robert but that wouldn't explain why the woman at the end just disappeared.
I just caught this movie on HBO, and I might have forgotten about the movie because I'm sure I seen it when I was younger. I have a bad memory when it comes to movies, especially when I have seen millions of movies. So, I'm not saying that this is a bad movie if I forgot about it, it's just that my memory isn't the greatest. I thought it was a pretty good movie for what it was.