@cjd Based upon what I've read of it, one guy who tried to kill another hacker is giving a couple of 34C3 talks, and the organizers knew about this well in advance, apparently with documented evidence.

If that's true - and I have no way of knowing whether it is - then the guy is an obvious security threat. It raises the question of how decisions are made about who gets to do talks and whether there is anything in place to keep known bad guys out of congress or at least to warn attendees about them.