The Crimes of Captain America
NRAMA: Let’s move to some of the details of the story. First off, what specifically is Cap being arraigned for?
EB: Whatever he was arrested for at the end of Civil War. You'll have to ask Tom Brevoort. I would guess it was being in violation of the SHRA and leading the rebel forces, though.
Brubaker's one of my favorite writers right now, so I choose to blame Marvel higher-ups for this confusion. One can actually imagine the same Q&A between Brubaker and his editor:
Brevoort: "Once Civil War is over, you'll need to incorporate the fact that Cap's been arrested. Maybe you should start off by showing his arraignment."
Brubaker: "What specifically is Cap being arraigned for?"
Brevoort: "Whatever he was arrested for at the end of Civil War. You'll have to ask Mark Millar."
This kind of exemplifies the pervasive legal problems of Civil War. For a crossover, and now a new status quo, that's entirely built around a controversial law, they just can't seem to decide on the basic details of the law. It's important that Cap gets arrested. It's not that important, however, to figure out what he's being arrested FOR.
However, I'm afraid I gotta give Ed the blame for what's next:
NRAMA: And the talking head’s comment of Captain America not going before a tribunal. Can you explain that a little more? As a military officer, the military legal system would have been the normal venue, right?
EB: Yeah, but Cap's military connections are murky -- he's not a Captain in the Army, for instance - and he's also a S.H.I.E.L.D. operative, which means he also works of the UN. I felt that because of the public attention to the entire Civil War that the government would want to make Cap's prosecution as open to the public and the common man as possible. So, since he's a figurehead and an icon, as well as all the other things he is, a trial in Federal Court seemed like a decent alternative.
What court Cap should be in depends a lot on what he's charged with. And we've just seen that that's pretty murky. Assuming that Steve Rogers is subject to the Uniform Code of Military Justice, he could be subject to a court-martial for certain crimes he commits. That's a kind of tribunal, but I don't think courts-martial are commonly called such.
Given the circumstances of his arrest, it makes the most sense, storytelling-wise, to assume that he's charged with something related to the Superhuman Registration Act. As the SHRA is a federal statute, violating it would then make a federal court the natural place for Cap's criminal proceedings. But I'm at as much of a loss for a specific charge as Brubaker is. The massive property damage to New York City, Cap's reason for calling off the fight, could certainly lend itself to some criminal charges, but Cap was the only one arrested, while everybody else got amnesty.
Maybe Millar meant for Cap to be charged with failing "to register," but that makes little (if any) sense. The government knows Cap's real name and identity. They always have. They know what his abilities are, and they gave him his shield. And it was the government that trained him, so he's presumably already met whatever skill standards the SHRA imposes. For all intents and purposes, he has already met the basic standards of "registration."
So for the lack of a better answer, I propose that Cap was being charged with what he did to SHIELD agents back in #1-2, particularly where he threw an agent out of a moving truck onto a highway, causing a pile-up. Despite being a UN organization, SHIELD clearly has some kind of relationship with the US government (as evidenced by the federal SHRA statute subjecting American citizens to conscription into SHIELD), so it stands to reason that assaulting SHIELD agents in the manner he did would be a federal offense.
Unfortunately, with Cap taking the eternal celestial dirt-nap, his prosecution is pretty much ended. That is, until "eternal" turns out to mean "temporary," in which case I expect the charges, whatever they are, will simply be dropped.