Noun and Chyba (2008, "Biotechnology and biosecurity") reviewed the risks of hostile uses of biotechnology in Global Catastrophic Risks (eds. Bostrom and Ćirković).
An excerpt from section 20.7 ("Catastrophic biological attacks"):
[M]odern society’s experience with bioterrorism has, fortunately, so far been limited to a small number of events that were neither intended to, nor did result in high mortality figures, so they may not serve as good indicators for what a successful major attack would look like. The 2001 US Anthrax scare that caused five deaths, for instance, involved a non-contagious pathogen, and although milled into a fine powder, the bacterial spores were initially contained within envelopes that resulted in only local dissemination. By contrast, the Aum Shinrikyo cult, seeking to stage a mass-casualty attack in order to realize a prophecy, attempted to disperse Bacillus anthracis, from a building rooftop onto the dense urban population of Tokyo. The Aum, which later succeeded in dispersing Sarin nerve gas in Tokyo subways, was, fortunately, unsuccessful both in efforts to procure a pathogenic strain of Bacillus anthracis, and in its attempts to efficiently disseminate the bacterium. But a more rudimentary dispersal technique was successfully used by another group, the Rajneeshees, whose actions were motivated by a desire to keep a large block of individuals away from voting polls, in order to influence local elections. In 1984, members of the Oregon-based cult successfully spread the enteric bacterium, Salmonella typhimurium, onto salad bars, causing illness in over 750 Oregonians and sending many to hospitals. Had the Rajneeshees used a more virulent pathogen, or had the US Anthrax been more efficiently dispersed, major public health disasters may have ensued. In 1993, estimates from the US Congress’ Office of Technology Assessment found that a single 100 kg load of anthrax spores, if delivered by aircraft over a crowded urban setting, depending on weather conditions, could result in fatalities ranging between 130,000 and 3 million individuals. However, these sort of dramatic results have been viewed as overly alarmist by those claiming that such high casualties would require optimal conditions and execution by the perpetrators, and that there would in fact be a very wide range of possible outcomes (Leitenberg, 2005).
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.