AMC has now set a late May 2013 bow for the third season, with development starting imminently. While Netflix's involvement isn't yet confirmed -- the deal hasn't been finalized -- it does seem as if AMC will be partnering with somebody to help share the costs, which seems to be the reason "The Killing" is coming back at all. As for the storyline, there's no word yet, however, Joel Kinnaman and Mireille Enos last we heard were apparently both already signed to return (though Variety suggests this may not be the case, but we can't really see the show happening without them) while Michelle Forbes and Brent Sexton may not come back. Billy Campbell is also uncertain at the moment.
Either way, "The Killing" really has to come back ferociously and with some purpose if it wants to survive past the third season. As we wrote about season two, "[it] soon turned into an irritating jerk around, resulting in a kind of blue balls for the audience." Hopefully the writers and showrunner Veena Sud have heard the criticism and are ready to have this show live up to its potential.