Aaron McLamb was cleaning a bookbinding machine in a Brooklyn factory when he happened to glance out a window and see history unfolding on the morning of September 11, 2001.

Then a 20-year-old volunteer at the headquarters of the Jehovah’s Witnesses, McLamb recalled that he momentarily turned away from his work and noticed a “very large fire” in the north tower of the World Trade Center, across the East River in lower Manhattan.

“I knew that this was gonna be something really big,” McLamb, now 45, told The Independent. He immediately got his 35 mm Canon Rebel 2000 camera and climbed to the top floor of the 10-story building, snapping photos until he ran out of film.

One of his pictures — of a lone fire truck racing across the Brooklyn Bridge toward the burning twin towers — is among the most remembered from that terrible day, symbolizing the bravery and sacrifice of the city’s first responders.

All six crew members on the Ladder 118 fire truck were killed when the south tower collapsed at 9:59 a.m. while they evacuated people from the adjacent Marriott Hotel.

A total of 2,753 people were killed in New York City after two hijacked passenger planes hit the towers, along with 184 people at the Pentagon and 40 victims on United Airlines Flight 93, which crashed near Shanksville, Pennsylvania, when the passengers and crew fought back against the terrorists. Nearly 10,000 more people have died from illnesses, many related to toxic air from at Ground Zero, in the years that followed.

Ladder 118, based at the Middagh Street firehouse in Brooklyn Heights, was crewed by Lt. Joseph Agnello, Vernon Cherry, Scott Davidson, Leon Smith, Peter Vega and Lt. Robert Regan. Two others from the firehouse — Capt. Martin Egan and Lt. Robert Wallace — also died that day but weren’t on the Ladder 118 truck.

They are among the 343 fire department personnel killed on 9/11, along with 37 Port Authority police officers, 23 city police officers and eight paramedics and EMTs.

On the morning of September 11, McLamb, an amateur photographer with a longtime interest in firefighting, said he was “intentionally shooting fire trucks” as he took pictures of the emergency response.

“I always wanted to be a firefighter, but I just never got an opportunity to go into that field,” said McLamb, who left New York City in late 2005 and now lives in Leland, North Carolina.

He recalled spotting Ladder 118 leaving its firehouse, and noted that the tiller-style truck, operated by drivers in both the front and rear, has “always been my favorite.”

McLamb said he watched the truck as it traveled “right underneath us on Prospect Street and circled our building, and then got up on the Brooklyn Bridge.”

“So, I was just waiting for them to get in position for that photo,” he added.

After the Ladder 118 firefighters arrived at the World Trade Center, they were helping others escape from the Marriott when the collapse of the 110-story south tower — more than a quarter-mile tall — buried them under thousands of tons of rubble.

The collapse created a “huge dust cloud,” McLamb said, and he and other workers watching from the 10th floor “were asked to go close all the windows in the whole building.”

“So that — that put a stop to taking any more pictures,” he said. “My final pictures, I think, were the dust cloud from the first tower falling.”

After all the windows were closed, McLamb said, everyone was sent home.

“I’ll never forget that part — walking home — because I lived further south than most in Brooklyn Heights…and the dust cloud and the debris cloud was actually in that area,” he said. “It had already subsided, but the damage was done.”

McLamb recalled walking through “at least an inch or two of dust on the ground” and “watching my feet kick up all this dust.”

“It was everywhere. There were papers everywhere, like office papers, 8 1/2 by 11,” he said. “Some of them were burned, some of them were not, some of them were just fine.”

In retrospect, McLamb said, he wished he’d “picked up some and, you know, see if I could get them to any of the names of the people that were on the, on the papers, or maybe their families or something.”

At the time, McLamb lived in a Brooklyn Heights apartment building with other Jehovah’s Witnesses from around the country who got free room and board in exchange for their volunteer work. Like millions of others around the world, he spent the rest of his day watching live TV coverage of the horrifying events.

During the next week, he had his film developed and the photos printed. Word spread through the neighborhood that not one of the Ladder 118 truck crew had “come home,” he said.

McLamb decided to bring his negatives and some prints to the firehouse, which he’d always intentionally walked past on his way to work so he could wave and say “Good morning” to any firefighters outside.

When he showed up at the firehouse, McLamb said, the firefighters were initially “kinda incredulous” until he explained how he’d “watched the truck leave the station” before taking the photo.

“Once they figured out that I knew what I was talking about, then they got out a magnifying glass, and they started realizing really quick that, yeah, I really did capture 118,” he said.

In a separate interview, retired Ladder 118 firefighter John Sorrentino told The Independent that although the numbers on the truck aren’t visible, it’s one of only a handful of tiller-style models in the city. In addition, Sorrentino said, crew members had mounted an exterior box on the truck’s right side.

Sorrentino, who was off-duty on September 11 but raced to the scene to help out, said he remains haunted by the sound of alarms worn by the hundreds of firefighters who were buried under the rubble.

“We knew what that sound was — and there was nothing we could do about it,” he said, adding that the feeling of helplessness was “the one thing that — that really sticks in my mind about 9/11.”

Less than a month later, McLamb’s photo appeared on the front page of New York’s Daily News under the headline, “The last run of Ladder 118.”

After 25 years, McLamb said he’s grateful he could document the doomed crew’s heroism.

“Part of my identity as a Witness is I try to help people as best I can,” he said. “So, I knew that I had an opportunity to help those families and the coworkers of the firefighters that didn’t come home because I had this picture.”