In reference to the Joker accusations, according to this article that's not true, at least as far as being in makeup is concerned:
"In New York City, Police Commissioner Raymond Kelly said: "It clearly looks like a deranged individual. He has his hair painted red. He said he was the Joker, obviously the enemy of Batman."
Oates would not confirm that information, but did say he spoke to Kelly. Asked whether Holmes had makeup to look like the Joker, Oates said: "That to my knowledge is not true."
In regards to the media somehow being responsible, I've never believed in that sort of reasoning, especially since it's been proven time and time again that it's not. A Batman movie no more played a part in this massacre than A Catcher In the Rye did in Mark David Chapman's assassination of John Lennon or the White Album did in the atrocities that the Manson family carried out. These people were nuts and would have carried out these acts of violence with or without the presence of books, movies or music. If indeed you believe a Batman movie is all it took to push this guy over the edge, what exactly do you propose should be done to prevent such tragedies in the future, ban all media? If it was somehow proven that a movie like The Dark Knight Rises was all it takes to set these lunatics off, don't you think we would see this sort of thing on a massive scale? The media might make for a convenient scapegoat but it's not what's at the center of these sorts of tragedies, it's the mental instability of the perpetrators and in the case of Columbine and similar cases, very questionable parenting.