He is both. He is a stupid kid (although I have seen evidence that contradicts this somewhat) that is responsible for some deaths, numerous cripplings, and many more injured. They are not distinct people.
I haven't really contradicted that though I dispute the term "fanatic".
No he is a fanatic. It certainly is his brother's doing that he is a fanatic, but he is definitely a fanatic. There was a small but growing train of evidence that he was, or was becoming, more fanatic then his friends thought.
I've seen fanatics (radical Islamists), spoken to them, been on their forums etc and Dzhokhar Tsarnaev wasn't really one of them. I've read the articles about him describing his world view on social networking sites as "Islam" and stuff like that, but really if you deconstruct it I'd say most of that came from his brother and wasn't really all that solid. You know, it's not as if he's sat down, thought it through etc. He may have been on that road but he's not a fanatic in the sense most of us are familiar with. He's a much more pedestrian kind. The slow witted, impressionable kind, perhaps.
I'm not doubting his Islamist credentials, you see. You can't just label people in that way though as "fanatics" otherwise you're putting him in the same camp as Osama bin Laden, there are subtle differences.
You know, maybe in another world where he and his brother could have grown up in a secure, secular Chechnya, either within Russia or outwith, there would have been no Boston Bombings.