I don’t know the relevant laws there - but I am certain that an autopsy would have been done? Beyond that, what more could be done? If that means a more expensive autopsy, then yeah they should do that - even Boeing might agree on that point, to help absolve them, even if they did somehow give the bacteria to the guy, but like if they were confident that it could not be traced to them in that manner.
Speaking of, even if they were guilty in this second case, that’s a very different thing than someone being able to prove it. “Innocent until proven guilty” is a foundational bedrock principle in the USA, and we cannot simply throw that away without losing something precious.
And with them being military contractors, they probably have classified status to where local police can’t just go subpoenaing their records willy nilly. I could be wrong though. Then again, if they are used to dealing with the likes of e.g. literal Russian spies, then surely they would be smart enough to not leave a paper trail on something like this to begin with?
But the first guy should already be enough to start an investigation. The second guy… I dunno what that one means, maybe yes but also might not be.