The child was sick, that I do agree with..I don't know what kind of relationship his family had. Even if he did have siblings, he probably wouldn't have been sharing a room, I just find that an 'astounding' leap as well!!
And if he was sharing a room he would have probably found out another way to carry out his plan.
Again, how you leapt from Dylan Klebold’s only-childness to “all only children” is astounding. Why don’t you just admit you over-reached and let it go, instead of trying to justify it?