"Crazy, or not crazy, that is the question!" Moussaoui cried framing the theme of a lawyers' joust over his mental state, as his court-appointed defence team strove to convince jurors to spare him from execution.
Eminent psychologist Dr Xavier Amador, called as an expert witness by the defence, endured an all-day grilling on the witness stand, on his four years of research which brought him to a diagnosis.
Moussaoui seemed at various times intrigued, bored and amused at his metaphorical session on the couch, several times shaking his head, and grinning.
’Beautfiul mind’
In an earlier comment, also flung towards the public benches after the jury had left court, Moussaoui, the only man charged in the United States in connection with the September 11 attacks, even diagnosed himself.
"Beautiful terrorist mind!" he shouted, with a smile on his face.
Dr Amador had on Monday referenced mathematician and schizophrenic John Nash, subject of the Oscar-winning movie "A Beautiful Mind" starring Russell Crowe.
Dr Amador described a healthy human mind as one where bits of information are strung together in a sequence, and so make sense, as in the scenes of a movie.
"His movie is like you have scattered all the pieces up on a table and try to make sense of it," he said, referring to Moussaoui.
Dr Amador said Moussaoui's delusions that his lawyers were trying to kill him and belief that President George W Bush would free him from jail, before he leaves office in 2009, and other behavior, all added up to a diagnosis of paranoid schizophrenia.
He argued that Moussaoui's frequent reversals of position, during his trial, including his claim that he was a key part of the September 11 plot, were more evidence of delusions.
At first "he absolutely wanted to make clear that he had nothing to do with it. We have seen the flip flop in this courtroom very recently. He is saying he had everything to do with it," Amador said.
The psychologist, author and academic saw prosecutors try to descredit him over his comments to the media on the case, and his description of a visit to Moussaoui's cell, when the Frenchman spat water all over him.
"This episode is not so much that he is crazy -- he just wanted to get rid of you," Prosecutor David Novak said.
Moussaoui outbursts
Dr Amador did admit under cross-examination that he had conducted several interviews with media outlets after Moussaoui's defense team undertook that any future comments on the case would take place in court.
Mr Novak also argued that Moussaoui had acted properly in court, choosing not to repeat earlier outbursts, apparently seeking to establish the Al-Qaeda plotter was in full control of his mental faculties.
Prosecutors are expected to introduce their mental health experts who have concluded that Moussaoui does not suffer from mental illness.
Dr Amador testified that Moussaoui's fervent denials that he suffers from paranoid schizophrenia are a symptom of the illness.
On Thursday, Prosecutor Robert Spencer asked Moussaoui if he was "crazy" -- he replied "Thank God, I am not."
Judge Leonie Brinkema, meanwhile, is expected to tell jurors Wednesday they are unlikely to get the case until next Monday at the earliest, after defence arguments dragged on longer than expected.