What's scary about this, is I bet dimes to donuts they'll do a 'psych evaluation' of this kid and he won't have a clue why he did it. He'll say he doesn't know. Probably pass a polygraph. That's the way it goes in a lot of these cases.
He admitted following her into the bathroom. Punched her in the face then slashed her throat with a box cutter. Put her in a bin and wheeled it out. Then he went and saw the new Woody Allen movie. It's cold. A certified psycho it seems. Doesn't appear to be a motive yet.