I guess I had let it go unnoticed, but the book apparently is compartmentalized in parts. Part one, Butterfly. Butterfly included the event, the immediate effects, and Caleum and Maureen's downfalls. At the end, Mo decides she can't stand it living in Colorado anymore and they decide to move back to Caleum's roots in Connecticut. I believe the actual idea for naming it 'butterfly' comes from the conclusion chapter. At a gas station, Caleum runs into a substitute teacher from Columbine. He recognized him from his revealing confessions about his fear of becoming a father at the Columbine recovery session held at the school. During Caleum and the sub's conversation a 'cabbage butterfly' softly landed on the sub's shoulder. it went by unnoticed. Right as the sub thought he was feeling excited about having his first child with his girlfriend he expresses feelings of fear, fear that his own son will turn out like Dylan or Eric. Caleum reassures him, even though he knows nothing about fatherhood. Caleum then asks him who he had been subbing for that day and it turns out that he had been the sub for Caleum's English class. The butterfly gets shooed away.
Part Two: Mantis.
It opens one year after the event. Mo's answering a questionnaire about her trauma. An evaluation maybe. For the first time we get to see the clinical side of Mo's PTSD, besides her Xanax abuse. This woman is really messed up in the head. She's got some problems.
Caleum's cleaning out a drawer at the farm, he comes across his old date book where he kept to do lists and important dates. After the event there weren't many entries, except for one written on July 29, 1999. Caleum reflects on that day, it was a day on the road coming from Colorado to Connecticut. They stopped at a Cracker Barrel, he chased the dogs outside to get them some exercise while Mo stayed inside, attempting to eat. He noticed she was completely unaware of what was going on. He called it 'psychic numbness.' As he reflects on the passage he lets the reader know that that was seven years ago.
Caleum starts to show his own obsessive compulsive tendencies. He keeps all old news clippings of the Columbine event stored in a large Tupperware container. Every once in a while he'll get drunk and stay online for hours, just searching and searching for info on the boys. Searching for some way to eliminate the troubles that are taking control of his and Mo's life. He describes the weapons they used. The way they dressed in Nazi-like attire. The way they got a hold on the guns they used. They're not you're typical evil monster, but the reality of their terror makes them even more scary.
Caleum becomes obsessed with connecting Chaos Theory to Dylan and Eric's actions. He's persistent, almost too persistent.

A note: I don't know if I can refer to them by their first names anymore. It doesn't feel right.