I don't think harrison has a dark passenger though. He was just a teenager who was angry and hurting. Probably needs therapy but not a killer.
I did wonder if they were implying that the police chiefs daughter was pregnant with his child though. With the wording on the voice-over when he was passing outside her house.
Also, just a thought but, thet could easily do a second season where they flashback to show dexter putting on a bullet proof vest at the police station. Think about it, he has to convincingly fake his own death, otherwise the police will never stop looking for him. He'd be all over the news and found in a week. And the blood...hmm...could he have got that from the butchers place they were showing (where the guy was chopping up deer outside) ?