Only known 9/11 footage from inside tower during attack resurfaces 25 years later

In the summer of 2001, brothers and filmmakers Jules and Gédéon Naudet were working on a documentary which followed the life of a probationary firefighter in New York City.

But the film they would end up making would be one of the most haunting accounts of the attacks on the World Trade Centre.

Released in 2002, 9/11 includes the only known footage captured inside the lobby of the Twin Towers as the attacks were unfolding, as well as reactions from everyday New Yorkers witnessing the atrocity.

"How bad is it up there that the better option is to jump?"

On the morning of 11 September, the brothers separated, with Jules granted access inside the building alongside Chief Joseph Pfeifer, allowing him to document the chaos and confusion inside the building's lobby.

(CBS)

The footage which Jules was able to capture featured some of the most sobering moments in the documentary, as firefighters realised the repeated crashing noises were the sounds of people jumping to their deaths from the 78th floor and above.

"You don't see it, but you know what it is, and you know that every time you hear that crashing sound, it's a life which is extinguished," Gédéon explained in the documentary.

"It's not something you could get used to, and the sound was so loud."

He wasn't the only person who was left shaken by the sounds, with Joe Casaliggi later recalling: "I just remember looking up thinking how bad is it up there that the better option is to jump?"

Gédéon's location also showed visible damage to the building's lobby, which was later revealed to have been caused by jet fuel which had travelled down the elevator shaft in the North Tower and exploded, leaving a scene of chaos in its wake.

Smashed windows can be seen in the footage, while Gédéon recalls seeing two people who had been burned by the explosive fireball.

"To my right there is two people on fire, burning," the filmmaker recalls in the documentary, explaining why he made the decision to deliberately turn his camera away.

"I just didn't want to film that... No one, no one should see this."

(CBS)

Before arriving at the building, Jules had also been in a unique position where he captured American Airlines Flight 11 colliding with the North Tower, becoming one of three people to do so.

Back at the station, Gédéon became increasingly aware that his brother would likely be filming at the World Trade Centre and wanted to get to him as quickly as possible.

"I'm supposed to be the big brother, so I'm completely responsible for Jules," Gédéon told NY1 while reflecting on the 25th anniversary of the tragedy last month .

Creating the documentary together was also a way for the brothers to process the trauma they experienced from being at ground zero on that day. "To be able to see every second of what I lived through was difficult, but at the same time helpful into confronting my trauma," Jules added.

The brothers captured some of the most important footage from 9/11 ( JOEL SAGET/AFP via Getty Images)

Where can I watch 9/11?

The Peabody-winning documentary was originally aired by US television network CBS and is not currently available to stream on any major platforms, but physical copies can be purchased online.

Several people have also uploaded the documentary to YouTube, allowing younger generations to discover the film for the first time.