This is off the scale - no teen or young adult has the emotional maturity to pull this off without getting caught. The kid that could organize and execute something like this, get away with it, and keep quiet, would likely be a high achiever, and thus unlikely to do so in the first place.
What egotistical young man, influenced by PS2 and Hollywood, could keep quiet given the circus around him?
This is not Columbine, not even close - this is somebody with a mission
Harris and Klebold had a mission, too. They did some very elaborate, long-term planning to carry it out, and they pulled it off reasonably well.
The difference was only that they planned to die at the end of it -- and we don't know if this nutjob hasn't got the same idea.
If there are 2 of them as I assume, then they can talk about it among themselves all they want...