NEW YORK (AP) _ Critics were worried in advance about graphic images in CBS's documentary about the Sept. 11 attacks. Instead, it is the sounds that likely will linger.
The sounds resemble distant gunshots, sometimes accompanied by smashing glass. Each are bodies striking the ground outside the World Trade Center, and firefighters flinch at the impacts.
``You don't see it but you know what it is,'' filmmaker Jules Naudet recalled. ``You know each time you hear that crashing sound a life has been extinguished. You can't get used to it.''
CBS screened a copy of its ''9-11'' documentary Monday for reporters. It will air at 9 p.m. EST on Sunday, the eve of the six-month anniversary of the attacks, featuring never-before-seen footage shot from inside the World Trade Center before its collapse.
Filmmakers Gedeon and Jules Naudet were witnesses to history because they happened to be filming a documentary about a rookie firefighter in a battalion near the towers.
Some relatives of Sept. 11 victims had urged CBS not to air the program out of concern that the memory of the attacks was too fresh.
``This is a broadcast about strength and courage as well as remembering the pain,'' said executive producer Susan Zirinsky. ``I think the timing is right.''
The only visible injury seen is a firefighter's bloody face as he rests. A still photo of the lifeless body of Fire Chaplain Rev. Mychal Judge being carried out by firefighters also is shown _ just moments after Judge is seen silently praying inside the trade center's lobby.
The Naudets said they shot no gory footage that day, editing as they went along even though one of the first things Jules saw in the trade center's lobby was two women on fire.
``I glanced at it,'' he said. ``The image was so horrible that it was not something people should see or want to see. The decision was made on the spot.''
There are, however, numerous examples of profanity, probably unprecedented for network television. They begin with the firefighters' reaction to the first plane hitting the tower. Staring at the building, several exclaim, ``Holy (expletive).''
CBS conceded there were several discussions before it was decided to leave in the strong language. Narrator Robert De Niro warns viewers about it in the show's opening.
``The language was rough but the circumstances were rough,'' Zirinsky said.
The documentary follows, in narrative form, the experiences of Engine 7, Ladder 1 in lower Manhattan. It focuses on Tony Benetatos, a rookie firefighter. Much of the pre-Sept. 11 footage is poignant: a rooftop drill at dusk the night of Sept. 10, the lit World Trade Center towers gleaming in the background.
The Naudets caught video of the first plane hitting the trade center _ the only such footage available _ when they were following firefighters investigating a gas leak.
When the second plane hit, it was preceded by a sound like the whooshing of wind.
While Gedeon Naudet filmed outside, his brother followed firefighters into the first tower, filming as the rescuers mass in the glass-littered lobby and receive orders to climb the stairs toward where the plane hit.
Office workers are seen leaving the building, sometimes running. At one point, a rumor sweeps through the firefighters that a third plane is on the way. A building worker methodically checks through a loudspeaker to see if people are trapped in elevators.
CBS, working with the fire department, identified all of the firefighters shown in the lobby and said none of their families requested the footage not be shown publicly, CBS said.
Jules Naudet is rushing with his camera toward escalators when the second tower collapses. His video screen goes black then records an unearthly snowstorm of debris.
Firefighters shout warnings for everyone to evacuate, and Naudet follows several as they scout for a way out. The building collapses about six minutes after he leaves. Naudet falls to the ground behind a car, protected by a firefighter as dust and paper swirl around him.
The documentary shows the Naudet brothers _ who each thought the other was dead _ reuniting at the firehouse.
The film's second half deals with the aftermath, showing scenes of recovery operations, including some underground.
CBS ends the documentary by showing pictures of the 343 firefighters who died that day and appealing for donations to a scholarship fund for their families.