User blog comment:Ktrfgfg/Chapter 53 and chapter 54 predictions/@comment-178.37.45.193-20140203172122/@comment-93.209.62.234-20140204100813

I doubt the Supreme Commander is behind of this. He had the chance to hand Eren to the Military Police and gave him to Erwin. For the same reason I do not buy the (excellent) theory that the royal family is the evil force. They suspended Eren's royal summon to their court when they had an excellent chance to get hold of him after he had defeated Annie.

The building which Erwin entered was a copy of the Reichstag in Berlin, the German parliament. (Google it and compare the windows.) That doesn't have to imply anythng, though.

Levi might be a Titan shifter and Erwin could be aware of that. Levi was "discovered" by Erwin underground and Isayama has said that "Levi is much older than he looks". Ymir is also older than 60 years but stopped ageing when in Titan form. Levi could have done the same, but lost his memories.