CNN is drawing comparisons to Cho's videos and "Oldboy," even though the roomies don't know of him ever watching it. The image with the hammer and the gun to his head are all they've basically got, and that the movie is South Korean.
I've never seen it, but I've heard that it is good.
Apparently they were hearing cell phones ringing and buzzing from frantic parents on the bodies of the dead students as they pulled them out of the building.