I'd say impossible. Are there any similar cases where a government or a company succeeded?
(http://www.bbc.co.uk/news/technology-22368287)
They've since changed[1] their mind about this, but finding videos of real people being really killed is trivially easy for anyone. This isn't in some specialised guro community or a shock image on 4chan, these were distributed on a social network with a billion users.
[1] Weird that they had to change their mind because these clips seem pretty clearly to violate their rules already.