To wit, we ALL saw him do it...and he had accomplices.
Truth will out. A man in love would not have put the family of his beloved through what MS did, even if there were suspicions. But a family that knew Michael loved Terry would never have conceived of such a notion and flatly denied it...IF they had not had reason to. Michael gave them reasons to suspect in spades, and that tombstone is permanent evidence of that.
Interestingly, these accusations against MS did not begin until TEN YEARS after TS's collapse.