Not very long into the press coverage of the terrible tragedy in Oregon, the interview with the father of one of the survivors brought up the possibility that the gunman may have asked some of the victims if they were Christian. (I believe that has now been pretty much confirmed.) The “media” as the folks on Fox and Rush like to call them, reported that information but did not editorialize on it. Of course, Fox et al immediately used that fact to bolster their construct that Christianity is under attack in America (it is not as far as I can surmise from reading both responsible conservative and responsible progressive sources).
I think there may be another more likely reason the gunman asked this question and left witnesses alive to report it. We know from the gunman’s writings and postings that he felt unvalued by society and that he wanted to go out in a flame the way previous mass gunmen have. And he wanted to have his name plastered all across our media. One way to do that right now, is to inflame the populace by hitting one or more hot buttons that the media, both traditional and social, have to jump on. But he was not muslin nor black nor an immigrant (though I think he may be the son of an immigrant).
So it is reasonable that he might have decided to “call out Christians” as a way to improve the odds of the reporting on his misdeed staying on the screens for a longer time.