Who Says Assassination Targets Took Up Arms Against the United States?

Yesterday, in the course of defending the Obama Administration's policy of targeted killings of accused terrorists, including American citizens overseas, White House spokes-lackey Jay Carney vaguely cited "ample judicial precedent" for snuffing enemies of the United States. He did, however, gloss over a rather long and storied history of something called "due process" during the course of which the government is supposed to prove it didn't grab the wrong poor bastard, either by accident, or through malice. Here's how the exchange went:

Q    But let's be clear.  This is giving a legal justification for killing American citizens without any trial whatsoever, without any evidence.

MR. CARNEY:  Again, I would point you to the ample judicial precedent for the idea that someone who takes up arms against the United States in a war against the United States is an enemy, and therefore could be targeted accordingly.  That's I think established in a number of cases, and I'm not even a lawyer and I'm aware of that.

But how do we know the someone is being snuffed because he actually "takes up arms against the United States" and not because some facial recognition software went haywire or, worse, because he's inconvenient or offensive to U.S. officials in a way that doesn't legitimately command punishment? All we have is the word of the administration that enemies of the United States are being targeted for death. But the case hasn't been proven in any way that's open to scrutiny.

Yeah, due process is hard because you have to show your work and convince (supposedly) skeptical observers. It's supposed to be that way.