At 14 he should be tried as an adult, but not sentenced as one.
Here's a place, though, that with all the good intentions around, the government will screw it up.  At 14, the kid can be helped, but he won't be:  he'll either go to Crime U, and learn how to be a better criminal, or other ways to be a criminal, and learn that crime=status, or he'll be sent to some "reform" place where he'll learn to laugh at authority, and come out as much a delinquent as he went in, and likely with little further personal development.
Odds are he won't even come close to getting that he should, which would be a grounding in the reality that he owns himself.  He can't blame his actions on anyone else; he owns them.  He can't just get away without consequences, because those come with actions, and he owns them, too.  In an ideal universe, it would be possible to subject him to the very experience he put his victim through, to make clear to him just what it is that he owns.  As it is, what his victim, and the victim's family, went through and are going through should be made as real to him as possible, and it should be pounded into him that he won't get to just die, rather he'll have to live with it.  What he did should be pounded into him so deeply that it will be as if he had been raped -- a memory that won't leave him alone, won't stop haunting him, will ambush him at unexpected moments.
That, he deserves.  The victim of rape never asked for that burden, and the victim's family never asked for it -- but he asked for it.  By making a decision to end someone else's life, he asked for it, whether he knew it or not.  The rape victim doesn't own that nightmare, but the killer does -- he bought it, and owns it, and has to be made to own it if he's to be accepted back as a human being.