At dawn on September 11, 2001 in Mount Vernon, New York, a man wakes, dresses, pulls black high-top trainers onto his feet, kisses his sleeping wife and heads to work in the north tower of the World Trade Center. Meanwhile in Queens another man — a pastry chef at Windows on the World, the twin towers’ top-floor restaurant — puts on jeans, a blue checked shirt and a Casio watch handed to him by his wife. She drives him to the station, where he waves goodbye, disappearing down the subway steps.

In New York City and its suburbs more than 2,600 others get ready for work. They choose suits, chefs’ trousers, firemen’s uniforms, baseball caps, summer dresses, overalls. All of them will be dead by morning’s end. As many as 200 will die jumping from floors 99 and above of the twin towers, the clothes they put on billowing, tearing, unravelling as they fall for 10 seconds on a journey from life to death.

As television stations turned their lenses from “the jumpers” in horror, Associated Press photographer Richard Drew caught an image of a man in freefall from the north tower. Fire rained, screams and soot filled the air and people on the ground began to flee, but Drew stayed to photograph the falling.

Later, back in AP’s offices, one of his shots intrigued him: a man, seemingly composed, his neat form set against an endless background of glass and steel. It has a stillness, suggesting an almost private moment that left those who saw it feeling uncomfortable and voyeuristic. How could such a quiet moment occur on such a violent day? American Airlines Flight 11 had hit the north tower at 8.45am. The impact cut a swathe through floors 93 to 99, instantly killing hundreds, ripping through elevator shafts and leaving emergency exits from the top floors impassable.

Temperatures at the point of impact reached more than 1,000C. Inside fire spread fast — carpets, furniture, computers and the building itself incinerated, creating a whirlwind of thick, noxious smoke that plumed up through the top storeys. For nearly 1,000 people trapped on floors 100 to 107 there was no exit.

At 9.03am, with millions watching, the second plane hit. The 1,000 people trapped in the top of the north tower were joined by 600 in the south. Jack Gentul, dean of student services at the New Jersey Institute of Technology, got a call from his wife Alayne, 44, a senior vice- president of the Fiduciary Trust whose offices were in the tower.

“She told me smoke was coming in the room, coming through the vents,” he says. “Her breath was laboured. I asked her why she didn’t go down and she said it was really hot out there. I said, ‘Honey, it’ll be all right, you’ll get down.’ She said that she loved me and to tell the boys she loved them.” I said, ‘I love you too and to call me when you get down’.”

Alayne never called. “She was found on the street in front of the building across from hers,” says Gentul. “Whether she jumped, I don’t know. I hoped that she had succumbed to the smoke but it doesn’t seem likely. In some ways it might just be the last element of control, that everything around you is happening and you can’t stop it, but this is something you can do. To be out of the smoke and the heat, to be out in the air . . . it must have felt like flying.”

Not long after the first plane hit, people in the top floors — those suffocating, burning, as the floors beneath them caved — had began to jump. They continued to do so until the south tower fell at 10.05am.

Witnesses say a constant arc of “jumpers”, some with makeshift parachutes, was maintained for over an hour and a half. Estimates of their number vary between 50 and 200. In 2003 the American journalist Tom Junod wrote that if the larger number were accurate — which seems likely — then “between 7 and 8% of those who died in New York City on September 11, 2001, died by jumping out of the buildings . . . if we consider only the north tower, where the vast majority of jumpers came from, the ratio is more like one in six.”

But in the months to come, America — and the world — would avert their gaze from Drew’s photograph, self-censuring and remonstrating with those who chose to look. After its initial outing in hundreds of publications, the picture disappeared, hard even to find on the internet. But who was he, this Falling Man? An editor at the Toronto Globe and Mail put a reporter, Peter Cheney, in charge of finding him. “For two or three days I worked non-stop to track down who this person might be,” he says. “I had gone all over the city looking at the missing posters trying to find somebody who matched this particular image.”

He had the picture enhanced. “I saw that he was black or Spanish and had a goatee. He was wearing what looked like a restaurant worker’s outfit.”

Late one night he chanced upon a handbill in Times Square. “I had this instant sort of recognition. There was a number, so the next morning I called.” It led to a woman called Milagros, whose family had been desperately searching for Norberto Hernandez, her brother, the same man who had waved goodbye to his wife at the subway steps in Queens. Milagros said she had seen Drew’s photo and believed it was the 42-year-old chef. She invited Cheney to his funeral.