Howard Lutnick: "It doesn't make sense, it's so crazy"

He is the chief executive of Cantor Fitzgerald, a bond trading firm handling trillions of dollars every year.

One thousand of its staff worked on floors 101-05 of the North Tower of the World Trade Center, close to the point where the first plane hit.

Now 700 people are missing, among them Mr Lutnick's brother.

'Not one got down'

"I do not know of one of my employees who got down - zero," sobs chief executive Howard Lutnick.

Mr Lutnick only survived because he took his son to school that morning.

New York City Mayor Rudolph Giuliani consoles the mother of a missing Cantor worker

But despite the anguish, the remaining 300 workers have insisted on staying open for business.

"Out of 300 people that have lost their friends - they lost the person to their left, they lost the person to their right - and they call me up and say they want to go to work.

"I say 'why do you want to go to work. Let's just go to funerals'.

"And they say 'no, I can not stay home, I have to work I have to do something'."

Close to breaking down, Mr Lutnick says there is just one motivation for continuing to work: "We have to make our business able to care for 700 families."

Ripped apart

A Goliath of the financial world, Cantor Fitzgerald handled $50,000bn of business last year, acting as an exchange for the world's bond markets.

Evidence of its might was its location, the north tower of the World Trade Centre, proudly displayed in its corporate video.

A friend of a missing Cantor worker searching after Tuesday's atrocity

But Tuesday's attacks ripped the company's New York operation apart.

When the first plane struck, its employees were cut off with little chance of escape.

None of the firm's staff at work that morning are believed to have survived.

With more that 5,700 people still missing after the World Trade Center attack, the pain endured at Cantor Fitzgerald is just one company's suffering.

And with 435 firms once based in the twin towers, the human costs is too much for many to bear.