ABC reports that the killer’s roommate was aware of his plans — at least in the abstract:

[The] alleged gunman authorities say is responsible for killing nine people in a predominantly black Charleston, South Carolina, church Wednesday night, had been “planning something like that for six months,” according to his roommate.
Dalton Tyler, who said he has known [him] for seven months to one year, said he saw the white, 21-year-old suspect just last week.
“He was big into segregation and other stuff,” Tyler said. “He said he wanted to start a civil war. He said he was going to do something like that and then kill himself.”

Oh, okay then. And at no point did you think about telling somebody?

On Twitter, Jonathan Chait suggests that ”maybe you should move out, or even alert the authorities, when your roommate describes his mass murder plan.” I’d rather think so, yes. But if you don’t, perhaps don’t explain so nonchalantly that you knew all about the guy’s proclivities and that, all told, this wasn’t much of a surprise.