Why is the media listing a possible anti-semitic motive? Because there is an actual basis or more simply the school has a decent Jewish population and there is nothing else to do but speculate and make people scared so they will watch more news?
I heard, and again this is the rumor in the news, that he had written things about killing people at the school in his personal journals. Included in those journals were some derogoratory comments/threats regarding Jewish people as well.
Why is it that sociopaths keep journals?
Perhaps as a subconscious cry for help ?
Maybe they really want someone to discover that they are spiraling out of control but they lack the mental capacity to ask for help etc.
But then again the line between genius and mental illness is a thin one.