I just loaded up The Columbine Guide with Eric's sketches, and his school essay on "Nazi Culture"--which was very revealing in retrospect.
That's a napalm tank on Eric's back, which was one of his many grandiose ideas. He laughed about creating human matchsticks running around, but of course he couldn't invent the flame-throwers he envisioned. He couldn't even get the Napalm recipe to work, thank God.
The Nazi essay is revealing in very different ways. Read in retrospect, you can see how he is using the cover of the Nazis to turn in his own gory fantasies as school assignments. The opening paragraph about a stadium stacked to the top with dead bodies is his own fantasy and has nothing to do with Nazis, but they provide great cover.
Here's the first page. The whole thing is here, and many more of Eric's sketches here: