Certainly it's more conspiratorial to assume that his death had something to do with his research, or that he was secretly a some kind of Walter White character?
Being politically outspoken on an issue which is contentious in that area, and which has caused violence before seems like the most plausible explanation that I have heard so far.
No, it’s just sticking to the publicly known information. Not listing something isn’t saying it’s not a factor, it’s just literally going with what the police were saying: they didn’t have any information about the motive yet.