By Richard Allen Greene
BBC News, New York
Charles Lowry was sitting in a bus opposite the World Trade Centre when the first plane hit five years ago, he remembers.
Lowry wonders about the fate of a firefighter he met on 11 September
For reasons he does not understand to this day, he got off the bus and headed towards the plaza.
"It was astonishing how quickly the street filled up with debris, burning paper fluttering down," he says.
On the scene almost as quickly, he recalls, were police and firefighters.
"A fireman very profanely threw me out of the plaza. I think about that son of a bitch every day," he says ruefully. "I have no idea what happened to him."
Whoever that fireman was, his odds of survival were not good on 11 September 2001 - more than one in 10 of the dead on that day were firefighters, 343 killed in all.
Tributes to them were everywhere at Ground Zero as the fifth anniversary of the attacks dawned clear and sunny on Monday, from the 15-year-old high school student wearing an FDNY (New York City Fire Department) jacket to the poster listing the names of every fire department fatality.
Few managed to find solitude among the crowds
Firefighters came to pay their respects from as close as New Jersey, across the river, and as far as Italy, across the ocean.
But for all the uniforms, helmets and badges, they were only a small fraction of the number who came to join in Lower Manhattan's public grief.
Hawkers and protesters
Perhaps inevitably, the large crowds and the intense emotion attracted eccentrics as well as mourners.
Minutes before the memorial service began, a woman began shouting: "Don't hate nobody, love them - remember 9/11! This is the message of God!"
A crowd gathered to watch, photograph, heckle and argue, while an incongruous busker nearby played "Under the Boardwalk".
A street vendor hawked American flags - "One dollar flags! One dollar flags!" - for those who had not brought their own.
Conspiracy theorist protesters provoked angry reactions
The conspiracy theorists were also out in force, wearing black T-shirts saying "Investigate 9/11" and holding up signs saying "Dissent is patriotic".
"The investigation so far has been a cover-up," Brad Gordon said.
"I'm not saying controlled-demolition this or Dick Cheney that," he added. "But we don't know what really happened."
Some at the scene shouted out their support for the protesters, while others called them crazy in the strongest possible terms, and one shouted "take a one-way trip to Afghanistan!"
But despite the chaos, once the memorial service began at 0846 - the moment when, five years ago, the first plane struck the first tower - a respectful hush did fall over the area.
And the reading of names began, to the accompaniment of a solo cello.
Many of the readers added personal messages when reciting the names of their lost relatives:
Some wore T-shirts honouring the dead
"Your daughter and I miss you very much."
"My love for you is eternal."
"We all love and miss you so much, especially your new grandchildren."
Some of those who had not been invited to participate personally in the ceremony honoured those they had lost in that most American of ways: on matching T-shirts.
Groups of family, friends and co-workers roam the memorial site together with the names of the dead emblazoned on their backs or chests:
"Shawn and Lynn: Together Forever, Flight 175."
"Never Forget: 343. East Haven Fire Department."
"Philip T Hayes, FDNY: Forever & Always in our hearts."
The loss, the grief, the shock is raw at Ground Zero, five years after the event - and for most, it is very public.
But even amongst the throngs, some managed to find - or create - a still, small point to be alone.
One woman curled up at a spot alongside the fence around Ground Zero, an island unto herself.
She nodded when a passer-by asked if she was alright, but her eyes closed off any further inquiry.
She was still there half an hour later when the same passer-by returned, still sitting silently by herself, nodding again briefly that she was alright.
When the passer-by returned a third time, an hour later, she was gone.