No the media is not responsible for creating violence but they certainly help propagate it. Think about it, after Columbine how many school shootings were there? After the beheading of Daniel Pearle how many more journalist did AQ behead? Why are there so many copy cat crimes after a much publicized incident? Because people want attention and to get on TV.
I think if the media weren't so prevalent things like columbine would be an isolated event and not a national phenomenon