Why did the boys pick the library to die in?
They didn’t really premeditatedly pick the library. It just kind of ended up happening there since the library randomly became their epicenter of where most of “NBK’ took place. After the carnage happened there, Eric and Dylan decided to go downstairs and make one last attempt to get the bombs to go off in the cafeteria. Eric was obsessed over the fact that the bombs hadn’t gone off like they’d planned. When they still couldn’t successfully make it happen, they went back upstairs and ended up back in the library. The library is a very short distance from the top of the staircase so it’s easy to understand how they decided to go back there to check on the scene. By then, all their victims had cleared out the library side exit door and all that was left were the dead bodies. So, if they’d somehow expected everyone would still be hostage and hiding there, they were sadly mistaken. It was basically a quiet graveyard now. The library exit door was still open and it’s pretty certain they could see there was activity just outside including cops and rescue milling about. There is evidence to suggest they had a brief encounter with the two of the SWAT just outside the door. It was an exchange of gunfire. I also recall pipe bombs were tossed in confrontation with the SWAT. The boys went to the windows and decided to exchange fire with the cops. By then, they were acutely aware that the walls were closing in on them with the authorities and that they were very low on ammo. This is when they decided to find a far corner of the library to end their lives. So, basically their deciding to end their lives in the library just sort of played out that way as they were now at a substantial disadvantage and they could not risk being surrounded by SWAT and potentially maimed and apprehended.