How dense can you be? There was no trial for one reason and one reason only. The government would first have had to make the case that unilateral secession was forbiden under the Constitution. It was recognized that this would not be possible and exposing that fact would have opened an enormous can of worms. Apparently it was hoped that Davis and Stephans, who both appeared to be in frail health, would not survive their abominable conditions of incarceration. When it became apparent that they weren't going to die in the short term, there was nothing left to do but to relaese them.