9/11 plotter 'raised in violent family prone to mental illnesses'
Jan Vogelsang, a clinical social worker, said Moussaoui was in and out of orphanages for the first six years of his life. As a teenager in France, she said, he was rejected as a "dirty Arab" by the family of his long-term girlfriend, with whom he had lived and won dance contests.
Ms Vogelsang said at the start of her evidence to the Virginia court that she did not intend to make excuses for Moussaoui's terrorist actions but wanted to explain how he reached that point.
Moussaoui, born in France of Moroccan descent, was in jail in Minnesota during the 11 September, 2001 attacks.
The jury has decided that the lies he told federal agents a month earlier kept authorities from identifying and stopping some of the hijackers, making him responsible for at least one death that day and qualifying him for the death penalty.
Now jurors are deciding whether Moussaoui deserves execution or life in prison.
Ms Vogelsang said that Moussaoui's mother was beaten throughout her pregnancies - including six before she gave birth to Moussaoui, who first went to an orphanage when he was just four months old.
She added that Moussaoui's family was only nominally Muslim and celebrated Christian holidays because his mother wanted her children to integrate into French culture.
Moussaoui had taken the witness stand to defend himself for a second time on Thursday, when he revelled in the terrorist atrocity and mocked the victims and their families.
District Judge Leonie Brinkema cancelled an earlier order to compel the would-be shoe bomber Richard Reid - a Briton - to give evidence in Moussaouri's defence. The jury may instead hear a written statement to summarise some of what Moussaoui's al-Qaeda comrade would have said on the witness stand.
Reid is serving a life sentence in a prison in Colorado.
Moussaoui, who calls Reid his "buddy" from their days together in al-Qaeda training camps in Afghanistan, testified last month that he and Reid were to have hijacked a fifth plane on 11 September and flown it into the White House.