You know, no man is an island ABQ. No matter how you want to put the responsibility on the shooter themselves (which you rightly should) there is also the factor of that person being brought up in a way that allowed this to happen. they weren't cared for. they weren't watched out for. they might have been treated poorly. maybe they were ostracized or just never taught morality. who can say at this point. i guarantee it will come up as the investigation proceeds. you can't have everyone wash their hands of blood just because we didn't pull the trigger. we let him do it.
at this point, my guess is it went down like this: the guy gets shafted by the girlfriend. he's feeling really fucked up, he has no one to turn to. he has no one to talk about it with, and doesn't know how to deal with his emotions of loss and rage. he decides to get revenge and make the cause of those feelings go away. he goes and gets a gun. maybe he has it already. this is how they do it on tv afterall, right? he goes and confronts the girl, probably says something like "this is what you get bitch, see what you made me do!?" and kills her. the RA comes down the hall because of the commotion, all "WTF just happened". the shooter turns and sees a witness. bam. he's dead. the shooter has to make his escape so he leaves the building quickly. but he's not satisfied. his crime hasn't erased his pain. he needs to make more people pay. he still has no one to talk about his thoughts with, or about what he's done. he goes to the classroom where maybe her new boyfriend is. he doesn't know who the guy is. maybe he does and he can't have them all watching him kill the kid. so he tries to kill them all. but even now, with blood and death his reality, he's not sated. his pain is too intense, so he kills himself.
think of just how many different times in this idiot's life he could have turned from this path if only people gave him the time of day. we're a bunch of sick fucks really. we don't talk to each other, us humans. we just sit next to each other on the bus, everybody with their ipods blasting, heads down, thinking inwardly. we don't share things because that's perceived as weakness. we isolate ourselves more and more. television reinforces this "we don't talk, we just watch" behavior. we learn to criticize and ridicule others. we take joy in it. american idol. we sensationalize and dramatize the failed relationships of others and of celebrities. we glory in it. britney spears. we are disturbed beyond words, and yet there are humans who indifferently claim no responsibility for the degeneracy they help foster. we as humans create monsters, and then take no responsibility for their actions. Mary Shelley knew exactly what the problem was.