When Steve rescued Bucky from the camp, he sees him lying on a table. We were never really given a clear answer. The movie might trick you into thinking that he was extracting him for information.
My theory: he was being experimented on by Zola. He did seem to show some jealousy towards Erskine. He may have created his own brand of Super soldier Serum and tested this on Bucky.
We never really saw what became of Arnim Zola in the First Avenger. Although, my guess is he is freed after giving the information of Red Skull’s base resulting to the final battle.
My theory: as he is the only one left who knew about where Bucky fell, he probably went back there to extract him and finish his work on the soldier making him an agent of Hydra.
There was a quick Easter egg in TFA where we saw a design of Zola robot form.
My theory: I wouldn’t put it pass them that we may able to see him in modern day in his robot form, prolonging his life. It is also a good way to maintain Hydra’s organization alive through him. We may see him as the main antagonist or second fiddle to the film’s antagonist… Maybe Baron Zemo.
Falcon
My theory: now they might change his origin for this film. So the only way I can fit him in is this… Aside from Captain America and Arnim Zola the only people who still knows what happened on the train skirmish, there is another man left. You guys remember Derek Luke’s character Gabe Jones? He maybe related to Falcon who could fill in the blanks for Roger’s when the subject of Bucky comes up.
Anyway, that’s all I got. What do you think?