I think it was because they were catching on to the fact that big pharma has started using nanobots to make us sicker. I think that is why so many microbiologists are being killed as well, cuz they have equipment strong enough to see the nanobots and were starting question what those were doing in our bodies. So to stop them, they killed them plus it would also serve as a warning to all the other microbiologists to shut up about what they're finding.