In a bit of Mockingjay mystery casting, it was just announced that Robert Knepper would be joining the cast of Mockingjay Parts 1 & 2 as Antonius. The mystery: there is no Antonius in Mockingjay!
UPDATE: We've confirmed with Lionsgate that Antonius has been added to Mockingjay as a new minor character created for the film. He'll be President Snow's Minister.
Knepper is probably best known for Prison Break, but has been in a million things and is currently on the new TNT show, Mob City.