I think that some things have to be stressed.
1. This isn't the worse school killing. The worse school killing was the bombing of a school house in Bath, Michigan, back in 1927 that killed 45 people mostly young children and injured 58.
2. The terrorist on 9/11 didn't have a single firearm between them and they killed 2,973 people.
3. The Oklahoma City bombing claimed 168 lives no firearms were used there.
4. There have been various serial killers that never used a firearm.
5. The last major University shooting was in 1966 when Charles Whitman killed 15 people at the University of Texas at Austin. One of the things I believe prevented him from killing more was the response by armed citizens with rifles that kept him from being able to take long distance shots by pinning him down allowing police to move in on him.
The thing is that this kid had already called in bomb threats and played with fire in his dorm. He had it in his head to kill some people and he had MANY options available to do that on a campus where no one was armed. If you couldn't have purchased the firearms he wouldn't have said "Oh shucks, I guess I wont kill anyone and live a normal life."