"John's" testimony was part of the defense's case that federal authorities missed multiple opportunities to catch hijackers and perhaps thwart the 9/11 plot.

His testimony included an e-mail sent by FBI supervisor Michael Maltbie discussing Moussaoui but playing down his terrorist connections. Maltbie's e-mail said "there's no indication that (Moussaoui) had plans for any nefarious activity."

He sent that e-mail to the CIA even after receiving a lengthy memo from the FBI agent who arrested Moussaoui and suspected him of being a terrorist with plans to hijack aircraft.

Prosecutors argue that Moussaoui, a French citizen, thwarted a prime opportunity to track down the 9/11 hijackers and possibly unravel the plot when he was arrested and lied.

Had Moussaoui confessed, the FBI could have pursued leads that would have led them to most of the hijackers, government witnesses have testified.

To win the death penalty, prosecutors must first prove that Moussaoui's actions ¡ª specifically, his lies ¡ª were directly responsible for at least one death on Sept. 11.

If they fail, Moussaoui would get life in prison.