Alexandria, USA - Jurors heard testimony from cult expert Paul Martin, an Ohio psychologist who said Moussaoui was "swept away" by Islamic radicals when he moved from France to England in the 1990s.
Martin said Moussaoui likely found "a sense of belonging" among the radicals who purported to represent a pure form of Islam.
"They come from a community that's been kicked around," Martin said. Moussaoui and the recruiters had a "feeling they've shared the sufferings of their own heritage," he added.
Martin said Moussaoui felt a need for social respect and to feel valued after he moved from France, where he had a fractured family life and no religious grounding.
"He's away from his family, he's lonely, he doesn't have any friends," Martin said. Moussaoui smiled and nodded his head.
Martin said that these factors, as well as Moussaoui's economic hardship and inability at first to speak English, made him vulnerable to recruitment by radicals.
Martin has not interviewed Moussaoui and conceded some details of his al Qaeda recruitment remain a mystery.
"You're not testifying al Qaeda is a cult, are you?" prosecutor Robert Spencer asked. Martin replied that the terror group is "similar in how cults recruit."
After Martin's testimony, defense attorneys read the jury a declassified CIA report from 2003 asserting that at al Qaeda's camps, "classical brainwashing techniques ... turned recruits into committed operatives."
"Time spent in Afghanistan mobilized, radicalized and transformed" them, the report said, adding that the brainwashing and isolation from families was designed to prevent "backsliding" by second-wave hijacker candidates.