I wonder if some of the vitriol is because people either didn't like Oscar to begin with, or because he was a symbol of hope and triumph over adversity and he has "let them down". There does seem to be a sense of taking this very personally in some areas on the net.
How we react is a very personal thing, as has been described today on here. I certainly don't think anything unkind about Reeva's mother's expression; equally I don't think anything unkind about Oscar's siblings' expressions.
I certainly, upon hearing the news that morning last year, could feel myself shaking my head, feel the sense of disappointment, and then growing horror as the day went on. And then explaining to DS how this man I admired had done something so terrible, but we don't know why, and that sometimes life coasts along nicely, but other times it all pivots and you have to reevaluate your thoughts, preconceived ideas, because the unimaginable happens.
I agree with Andrew Harding - this isn't whodunnit, it's why-dunnit.