It will be up to second amendment supporters to find them, before the left is able to impose its own agenda. In the end, though, it was Harris and Klebold who chose to leave this world while destroying Columbine High. They were free to stop at any time, up at least until the moment they marched into the school building and Eric Harris warned Brooks Brown to get out. They chose to kill. They wanted to kill even more.
Nihilism is the black hole of philosophy, liable to swallow everything that gets close to it.
Deny the free will of Klebold and Harris, blame their actions on music, the school, the ready availability of guns, and all you will do is feed the despair. We might, repeat might, be able to prevent this sort of thing from happening again. But we cannot let ourselves think that guns or culture was the main cause of this crime. Harris and Klebold had free will. Even as the mayhem began Eric Harris chose to let Brooks Brown live.