The article was an interesting perspective. Here we have a kid who actually carried guns and knives with him in school. He had violent thoughts, but in his case, nothing came of it. He is simply discussing what he was, who he became, and what he observes now as a high school teacher. It is worth reading and opened my eyes to a few things.
Personally, I think certain video games are a factor in mass shootings. I think drugs factor in as well. Poor parenting may also be a factor, and an individual's biological and mental makeup is likely the biggest factor.