"Walker's best defense seems to be that he only knew of them as conspirators after the fact, and feared any attempts to extricate himself from involvement "

If that is the defence, it looks a pretty solid one.

Whatever involvement the Taliban may have had with Al Qaida or whatever is pretty high level stuff, hardly of any relevance to charges against the equivalent of a private.

As for the prison mutiny or whatever it was, that is very murky territory. Given the way it panned out, it sounds suspiciously like a massacre in which some of the prisoners, having been allowed to keep their weapons for some strange reason, used them. More like Wounded Knee than anything. Maybe that wasn't how it actually was - but it doesn't, on the face of it, sound much like something where an insignificant prisoner (which is what Walker appears to have been) would have had any advance confirmation to give, even if he'd wanted to.

This just isn't something where talk of trials, let alone executions and so forth, makes any sense at all. Of course that doesn't mean it might not happen that way, but if it does it will be a real own goal.

Trials after all wars should be reserved for war criminals, whatever side they are on. Roll on the establishment of a properly organised international war crimes tribunal to help that along.