It’s not clear. What does seem clear is that you selected a detail, a minor point, to make your point on why the “detainee” aka terrorist just may not not need to testify while totally ignoring the larger point of the post. Why wouldn’t they want Abed to testify, and why is this going to trial?
On the contrary, that would be a major point.
But, as I said, much information will be missing now from news reports that will only come out in trial. That's to be expected.
However, when something is reported, then it's significant. And this was reported. So, in answer to your question of how they could have a trial without the detainee testifying -- that would happen according to the news report of this other person reporting it. That's one example that we've been given from the news report, and not something speculative.
And in answer to your question as to why the military might not want the detainee to testify -- as I said earlier, it would be to totally control his environment and to make him understand that he's totally under the control of the military, in order to get good intelligence out of him over the long run.
....and as to the question of WHY the military should send these Navy SEALs through a court martial to begin with, given all we DO know about this “detainee”.....you have not answered (at least from what I can gather by your posts).