I believe when Eric and Dylan met with Mark Manes on 4/19 to get the last of the bullets etc. Mark asked Eric if he was going shooting that afternoon/evening and Eric said "Maybe tomorrow"
I am wondering in AMR when Sue wrote about Dylan mentioning a senior prank and then saying "you'll see" if he was talking about an actual prank or if he was telling his mom in a way what he was going to do. Also some speculate giving her a journal with the rendering of "The Scream" was foreshadowing but I think Sue just really liked art, she is a painter.
Also in Dylan and Zach Heckler's college admission essays to The University of Arizona they both talk about a big production in April. Probably Smoke in the Room or Oklahoma but Dylan probably added it to be cheeky so to speak.
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"And you know, you know, you know, this can be beautiful, you say you're numb inside, but I can't agree. So the world's unfair, keep it locked out there. In here it's beautiful."