I did a big research paper on the topic of mass shootings in college to support my position that it isn't guns that's the issue. I mean, we had shooting ranges/classes at schools back in the 50s and 60s.
The reality is, mass shootings were crazy rare until the 80s/90s. What changed? Guns had always been around. Columbine really changed the game. I can't recall but there were a lot of studies done that showed how many copycats and attempted copycats that came from Columbine.
A few things changed, in my opinion. It was the 24/7 media coverage and turning a nobody into a name over night, which was actually cited by the Oregon community college shooter as an inspiration. And the fact that our source of entertainment and desensitization to violence and gore and murder is fascinating. I'm not saying everyone who plays video games is going to kill someone but for disturbed individuals, it serves as some type of sensation and fantasy.
Also, there's a staggering amount of the younger shooters that were hardcore gamers and on psych meds.