This is obviously just MOO:
I feel some of the reason why there is so much doubt in the ruling of his death is in part because of the weirdness (?) that has surrounded this case. The contradictions on Harley's medical background, the odd way the Chief handled SM and "protected" the family instead of giving straight answers, the all together so many unanswered questions that still linger in the air for some.
I know PCPD doesn't owe the general public every single detail, but I think if they released some more info, especially the stuff that make them so sure it was nothing but a tragic accident, people would back off and accept that it was nothing but a horrible horrible accident and not nefarious.