I don't think anyone needs to ransack a teenager's room, but as parents, we need to stay vigilant and be parents, and it is possible to do so and remain respectful of one's privacy - whether it involves something like this with weapons and bombs in kids' bedrooms or drinking and driving. I had no reason to suspect either of mine were doing anything dangerous, but I did not hesitate to ask questions and to go into their rooms and sit and talk with them. We also ate dinner together at a table every night, even with sports and jobs, and talked to each other. FWIW, I became a single parent when they were in elementary school, so I was mother and father.
Hindsight is always 20/20, but it just seems that there were so many signs, both emotional and physical, with Kleibold and Harris that were either overlooked or ignored. Hopefully this has opened the eyes of those involved with kids, inside and outside the home, that being proactive is okay.