I Have It!
I know who the traitor is! I KNOW!
In the original Avengers Loki was controlling the Hulk to lure Thor into a trap. I am seeing the same parrallels. In 'Dead Man Walking' at the end, we see Hank Pym and Bruce Banner conversing about giving credit to Hank for the super-soldigers. And Hank says he'll be gone in a month. He explains why and states "Look who they're phasing out." The last shot is Fury in the security room watching the two. At the end of "The Trial of The Incredible Hulk" Hank gets a message from a man, whoes face we do not see. This man is Bruce Banner.
Now what does this mean? Hank talks with the traitor, whom we see to have small hands and pretty lanky, which is why some of you don't believe it could possibly be the Captain. I believe the traitor is.... Bruce Banner. It was Hank who released the secret files to the media. He and Bruce planned Banner's escape from the beginning. That's why Banner calls Hank at the end of Ultimates 2 #3 and thanks him. Remember it was Hank who was in charge of sedating Banner and assures everyone that he's doped Banner enough. As we see that is not true, cuz he wakes right up.
Loki played his cards right to make it look like Thor released the files. And Send the Ultimates and The Union after Thor. Now that Thor is gone, Loki is free to create hell on earth. Then people would ask, how does banner get from The pacific island where he calls Hank, to Hanks appartment to show Hank what the Ultimates did in the middle east, to Nepal where he saved French explorers? Easy, it must frustrate you to comabt someone who can shuffle reality like a deck of cards in this three-dimentional realm. It's Loki.
The Red Skull, whomever he is, posing as one of the Ultimates, The Korean general, is in leauge with Loki and they get Ultron to help, and God knows whoever else that has already shown up. Just like the original Avengers, Loki has been using the Hulk.
If, for any reason there is a traitor on top of Banner, like the person killing is a different person from the one who released the Hulk files. The Red Skull is poseing as one of the Ultimates, not the acctual Ultimate. Maybe that's why he had to off Hawkeye, so he could pose as somebody. And Ultron, a simple re-programming and he belongs to the bad guys.