Judge Leonie Brinkema acted on complaints from the defence team and issued a stern warning to prosecutors before the jury was brought in on Monday.
But the advice did not lessen the emotional impact from more than 20 witnesses detailing the final hours of their loved ones, as prosecutors on behalf of the government seek the death penalty of the only 11 September conspirator to be tried on American soil.
Brinkema acknowledged that "there’s no way of avoiding some degree of emotion in a case like this," but said "the government is approaching shaky ground."
She noted the prejudicial impact can be so overwhelming that a death sentence could be overturned on appeal. "You may pay a price for that down the road," she said.
The jury will hear from family
members of 45 victims
Among the evidence heard on Monday was testimony from one man describing how his wife and brother were killed when dining in the Windows on the World restaurant atop the World Trade Center.
He told the jury he now cannot bear to see his wife's indentical twin because of the painful memories.
Perhaps the day's most dramatic testimony came from 73-year-old C Lee Hanson, whose granddaughter, Christine, at two-and-a-half, was the youngest victim of the attacks.
Hanson said his son, Peter, called him by mobile phone from United Airlines Flight 175 to tell him they had been hijacked.
Peter said he thought the hijackers were going to crash the plane into a building. "Don't worry Dad, if it happens, it will be quick," Peter added.
"As we were talking," Hanson told jurors, "he said, very softly, `Oh my God, oh my God, oh my God!' And there was a scream in the background."
Crying, Hanson added, "I looked at the television and saw the plane fly into the building."
No general release
Prosecutors say they have scaled back some testimony.
They have also frequently reminded the judge that they are presenting testimony form only a tiny fraction of those affected by the nearly 3,000 deaths that day.
So far, prosecutors are about halfway through the 45 victim-impact witnesses they plan to present to the jury. They intend to close their case on Wednesday.
"I looked at the television and saw the plane fly into the building"
C Lee Hanson, 9/11 family member
Late in the afternoon Brinkema said she had decided against releasing the cockpit recording of United Airlines Flight 93 to the general public.
Later this week, the jury will hear the first public playing of the tape from the jet that passengers tried to retake from the hijackers.
Because some Flight 93 family members objected to public airing of the tape, Brinkema decided that only the transcript, not the actual tape, would be released to the general public with other trial evidence.
Moussaoui, a French citizen born in Morocco, pleaded guilty last year to conspiring with al-Qaeda to fly planes into US buildings.
He was ruled eligible for the death penalty by the jury last week despite the fact he was in prison in Minnesota at the time of the 11 September attacks.