That makes sense. Whenever I follow stories like this, they often follow the same pattern. At first, the people interviewed say, "I never thought he would do this; he was so nice/normal." Then, a few days later, all the skeletons in the closest come out with all the warning signs.
Interestingly enough, I understand why people don't report those signs. There was a kid in college who had a mental breakdown and a few months later threatened to kill (mostly) everyone in our dorm. None of us who heard him say it reported it to anyone. We just tried to calm him down and then we ended leaving him alone to sleep it off. He never did anything, but I regret not doing more now that I'm older. It was just an awkward situation where someone who's upset just says something out of frustration and it's easy to brush off. Moreover, even if you do think it could be serious, you don't want to report him and then have that attention set him off. Ultimately, in order to get people to speak up, somebody has to change significant aspects of our culture.