Zackarias Moussaoui was arrested prior to 9/11 and could've cracked the whole case open, but unfortunately that was not the case.
He has stood trial and has received his verdict. The prosecution in his trial presented exhibits that we all can view here.
Among these exhibits, we can find the transcript of the United 93's cockpit voice recorder (one of the 2 black boxes found for U93) as "P200056T Transcript of Exhibit P200056" on the prosecution-link given above. It's a PDF of the transcript. Link to this exhibit directly here.
In this transcript you can among other things read someone (assume this is the flight stewardess) say no several times as well as other things.
Then you can go to exhibit P200080 and see a crazy letter written by Moussaoui himself where he among other things mocks this poor flight stewardess that begs for her life (he heard the actual recording played in the trial). You can also see his crazy BS about "truth" and even anti-semitism in the end. Once again, this is a PDF that will be downloaded when you click the link for (prosecution) exhibit P200080. The letter was written in 2003 after the events. One of the craziest letters I've seen. A link to P200080 directly here.