Some questions have arisen about why–as the news story indicates–if Moussaoui pleads guilty much of the government’s evidence of the 9/11 plot “might never be heard.” If Moussaoui pleads guilty, he will admit in open court that there was a 9/11 conspiracy, that he was a member of it, and that he took certain concrete steps to help carry it out. By waiving his right to a trial and admitting guilt, Moussaoui would relieve the government of the obligation to prove the charges–which would include proving that al Qaeda exists as an enterprise, that it plots terrorism, that it plotted 9/11, and how it executed the attacks. So, for example, if the government were prepared to present at trial the testimony of an accomplice who would describe all these various aspects of al Qaeda’s operations, Moussaoui’s guilty plea obviates any need to do that. There would, of course, still be a sentencing phase (i.e., a “death penalty trial”) before a jury. But the only issue there would be whether Moussaoui should be executed.
(BTW, in non-capital cases, there is no “trial” at the sentencing phase. The court alone imposes sentence at a hearing–no jury. While I am not a capital expert, I believe that U.S. law requires the sentencing phase in a death-penalty case to be tried to a jury–that is, I don’t even think a defendant can waive the right to a jury determination of the penalty (and even if he could waive it, a court probably would not accept the waiver since most judges would prefer not to decide a death sentence unilaterally, and the government probably would not accept the waiver because it often figures it has a better shot with a jury than with a judge.)
At the death-penalty phase, the government would not be required to present the evidence showing that Moussaoui is guilty of the charges in the indictment because he will already have admitted guilt at the guilty plea. Now, as a practical matter, to prevail in the death phase, the government will surely have to prove some aspects of the 9/11 plot–it has to prove what are called “exacerbating factors” beyond a reasonable doubt (basically, to show that they so outweigh any “mitigating factors” favorable to the defendant that the extreme penalty of execution is called for). But such a presentation would be much more streamlined than it would be at a regular trial in which the government would first have to prove the defendant was actually guilty.
A penalty phase is more about the defendant’s character and the particular heinousness of his offense than it is about showing how he went about committing the offense (the latter being what the trial is usually about). This would be a somewhat unusual penalty phase because the jury–unlike the jury in most death penalty cases–will not have first heard all the government’s proof of guilt. So the government will probably have to present a little more guilt evidence than usual, but it would still be nothing like the full-blown presentation at a normal trial where guilt has not yet been established.