As I know from my own case, even Snowden's own testimony on the stand would be gagged by government objections and the (arguably unconstitutional) nature of his charges. That was my own experience in court, as the first American to be prosecuted under the Espionage Act – or any other statute – for giving information to the American people.
I had looked forward to offering a fuller account in my trial than I had given previously to any journalist – any Glenn Greenwald or Brian Williams of my time – as to the considerations that led me to copy and distribute thousands of pages of top-secret documents. I had saved many details until I could present them on the stand, under oath, just as a young John Kerry had delivered his strongest lines in sworn testimony.
But when I finally heard my lawyer ask the prearranged question in direct examination – Why did you copy the Pentagon Papers? – I was silenced before I could begin to answer. The government prosecutor objected – irrelevant – and the judge sustained. My lawyer, exasperated, said he "had never heard of a case where a defendant was not permitted to tell the jury why he did what he did." The judge responded: well, you're hearing one now.
And so it has been with every subsequent whistleblower under indictment, and so it would be if Edward Snowden was on trial in an American courtroom now.
In addition, Ellsberg never got a "fair trial"; the charges against him were dismissed for gross misconduct on the part of the government -- see http://www.washingtonpost.com/... for a summary.