I agree your alternative theories are out there in the land of highly unlikely. I guess we can’t say they are impossible scenarios, but yes, very unlikely that the possibilities you outlined occurred.
Do you think it’s impossible that someone staged NO’s death to appear as a suicide, therefore fooling the ME into ruling it as such in error? Alternatively, do you think it’s impossible that the ME was encouraged/bribed/threatened to rule it as a suicide? Personally, I would put more money on the first of my two suggestions as a possibility, but I wouldn’t be shocked if it turned out to be the second either. Our law enforcement here has a horrible reputation for dishonesty and corruption. When this is the case for local law enforcement, people unfortunately begin to take anything they say with a huge grain of salt. I’m very thankful the FBI has stepped in, for whatever reason, just to be another set of eyes on the situation.