I feel for his family. Nobody wants to believe their loved one is capable of such a horrible thing. We see it all the time. A person is accused of heinous crime. Family members say "this can't be so" "He would never do such a thing."
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In my mind, denial is an expected response in such a situation. The heart and mind never want to accept such information about a loved one IMO.
His grandma doesn't seem to have any problems believing it.