The main thing I will always wonder, is what was going through their minds when they realized that the bombs weren't going to go off? What did they think when they looked out the window and saw all those students outside, people they intended on killing? Were they furious? Didn't care? They are infamous to this day, but killing practically everyone at Columbine would have made them legends for life. Their names would have been recognized well into the far distant future. They knew that, and they wanted to be above and beyond all of the previous school shooters that only murdered a handful of kids at most.
Even though they "only" killed 15, including themselves, they certainly made their mark. Eric and Dylan knew how to make people remember. They, especially Eric, made sure that plenty of material was left for us to work with. Trying to figure out a great mystery that will always be just that, a mystery. Like everyone else, the only thing I can ever do is speculate. And I will for many years to come because unlike the usual dull and detached murderers out there...Virginia Tech dude ring a bell?...Eric and Dylan drew us in permanently. 12 years and counting.