To look at it in another way, it is surprising that someone with that level of knowledge intent on killing people didn't kill far more people. There are lots of simple ways someone with decent chemical knowledge and access to lab equipment could kill a lot of people in a confined space, but instead he chose to use guns primarily.
My leading hypothesis would be that people in this sort of mental state are not motivated by maximising the number of people they kill but by fitting into the mold of a gunman or fulfilling some other psychological desire. So if that is the case we should be comforted that even if the access of people to dangerous chemicals increases they won't use them. What would be really dangerous is if someone psychologically normal decided to kill a lot of people.
A Ph.D student in neuroscience shot at least 50 people at a showing of the new Batman movie. He also appears to have released some kind of gas from a canister. Because of his educational background this person almost certainly knows a lot about molecular biology. How long will it be (if ever) before a typical bio-science Ph.D will have the capacity to kill, say,a million people?
Edit: I'm not claiming that this event should cause a fully informed person to update on anything. Rather I was hoping that readers of this blog with strong life-science backgrounds could provide information that would help me and other interested readers assess the probability of future risks. Since this blog often deals with catastrophic risks and the social harms of irrationality and given that the events I described will likely dominate the U.S. news media for a few days I thought my question worth asking. Given the post's Karma rating (currently -4), however, I will update my beliefs about what constitutes an appropriate discussion post.