Lawyers from each side will have one hour on Wednesday to put their final case before the jury starting at 1pm (1800 GMT) in a Virginia courtroom, a few miles from the Pentagon, one of the targets of the September 11 hijackers.
Prosecutors are expected to argue that Moussaoui lied while in prison in August 2001 to allow his 19 al-Qaida "brothers" the time to go forward with their plot to ram fuel-laden airliners into prominent US buildings.
The defence counters that Moussaoui was rejected by the "real terrorists" as a loud-mouthed nuisance, had no role in the September 11 assault, and that even had he told investigators that al-Qaida would use jets as missiles, disarray was so acute in the security infrastructure that authorities would have failed to thwart the plot.
Final arguments by prosecution and defence lawyers remain in phase one of the penalty trial, before Judge Leonie Brinkema sends the jury out to mull the fate of the defiant 37-year-old Frenchman.
Should the jury unanimously find Moussaoui's "lies" in jail in August 2001 safeguarded the plot and directly caused the deaths of any of the nearly 3000 people killed on September 11, Brinkema will convene the trial's second phase.
Moussaoui is the only man in the
US charged for the 9/11 attacks
Relatives of September 11 victims will deliver testimony on how the catastrophe shattered their lives, before the jury is again be sent out, to decide whether Moussaoui deserves to be put to death.
The jury was shown videotaped extracts of top US administration officials testifying to an official commission on US government failures that the September 11 hijackers were able to exploit.
If jurors decide after the first phase that the government has failed to prove Moussaoui, arrested before September 11 while learning to fly a 747 simulator in Minnesota, is eligible for the death penalty, he will spend his life in prison.
Moussaoui is the only man charged in the US in connection with the September 11 attacks.
The extracts from the hearings in 2004 featured Condoleezza Rice, who at the time was the national security adviser; George Tenet, then CIA director; and Richard Clarke, former White House anti-terrorism co-ordinator.
One of the final video clips was a film in which Clarke apologised to the families of the September 11 victims.
"Your government failed you," Clarke was seen saying.