The material, caught on tape by French filmmakers Gedeon and Jules Naudet, 31 and 28 respectively, is believed to be the only such video available from inside the complex after the planes slammed into it.
The broadcast will air on Sunday, March 10, at 9 p.m, the night before the six-month anniversary of the terrorist attack.
"It's something that's very vivid, very moving and very heroic," said CBS President Leslie Moonves. "I thought it was very important as a broadcaster to show this footage."
The Naudets were in lower Manhattan on the morning of Sept. 11, shooting a documentary on New York City firefighters. Hearing a roar above him, Jules turned his camera toward the sky and caught pictures of the first plane striking the trade center. He later sold the images to a video service and they were widely broadcast.
Both filmmakers rushed to the scene and kept filming, Jules inside the building complex and Gedeon outside. For a while, neither brother knew whether the other was still alive, Moonves said.
None of this other material has been broadcast. The brothers brokered the deal with CBS through friends at Vanity Fair magazine and its editor, Graydon Carter, who contacted Moonves.
The CBS executive would not say how much the network paid for the material. He said there was no bidding war with other networks.
The video is dramatic but not gruesome, said Susan Zirinsky, the executive producer of the CBS broadcast. "It is remarkable to be in the belly of the beast but it is not difficult to watch," she said. CBS News' Hal Gessner and Tom Forman will serve as executive editor and senior producer, respectively.
It's unclear whether the footage will show recognizable images of people who did not survive, which may be upsetting to family members. Firefighters who were at the scene are involved in putting the CBS show together, Moonves said.
The CBS executives said they are sensitive to critics who will be watching to see if the event is exploitative.
"All of us feel humbled by the goal of presenting this in the right way, in the right tone, in the right context," Zirinsky said. "Nobody is out for anything other than showing a remarkable body of work."
The Naudets hope that part of the broadcast will be used to raise money for family members of firefighters killed on Sept. 11, according to CBS.
It's the second high-profile TV documentary about Sept. 11 to be announced in recent weeks, but will be the first to air. HBO has a deal with former Mayor Rudolph Giuliani to air a documentary about the attacks and their aftermath seen from his perspective. It is scheduled for telecast on May 26.
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