Why is the category of 'capable of getting into a Ph.D. bio-science program' relevant? I can kindof see where you are going with this; it's easy to say that someone who can design something that could hurt a lot of people has better access and is therefore more likely to do so.
But while this is evidence that someone of the category you've named can want to engage in mass murder, it isn't evidence that he had better access or was more likely to do so given that he may have had better access. In actual fact, since the harm here largely involved a firearm and we don't know if the canister was even related to his bio-science program you should be updating downward on someone in that category relying on a biochemical agent rather than just using a gun. You have evidence that, even with a (perhaps strong) bio-science background people who engage in mass murder for what appear to be their own preferences just use a damn gun like everyone else with the same preference.
People who kill with guns aren't trying to kill lots of people. Mass murderers prefer armies, or if armies aren't available, bombs. A backpack-sized IED have killed more people than a gun.
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.