Jurors in the death-penalty trial of Zacarias Moussaoui deliberated for a third day Friday to determine whether the confessed Al Qaeda conspirator is eligible for the death penalty.

The jury had deliberated more than seven hours Wednesday afternoon and Thursday. On Thursday, jurors asked about the definition of "weapon of mass destruction." One of the three convictions for which Moussaoui could be executed is conspiracy to use weapons of mass destruction.

The jurors were told that a plane used as a missile — the tactic employed on Sept. 11, 2001 — qualifies as a weapon of mass destruction.

Moussaoui is the only person in this country charged in connection with the Sept. 11 attacks. He pleaded guilty in April to conspiring with Al Qaeda to hijack aircraft and other crimes. The sentencing trial will determine his punishment: death or life in prison.

The jury must find that Moussaoui was responsible for at least one death on Sept. 11 for him to be eligible for execution. If the jury finds him eligible for the death penalty, a second phase of the trial would be needed to determine the sentence.

Moussaoui was in jail at the time of the attacks, but prosecutors argue federal agents would have been able to thwart or at least minimize the attacks if he had revealed his Al Qaeda membership and his terror plans when he was arrested and interrogated by federal agents.

Also, court transcripts indicated federal prosecutors in Philadelphia have launched a criminal investigation of Transportation Security Administration lawyer Carla J. Martin. Moussaoui's death-penalty trial was nearly derailed after U.S. District Judge Leonie Brinkema found that Martin improperly coached multiple witnesses on their testimony and lied to defense lawyers.