Two years on, the identity of the Falling Man remains a mystery. But perhaps his identity isn't so important as what he has come to symbolise.

"Do you remember this photograph? In the United States, people have taken pains to banish it from the record of September 11, 2001. The story behind it, though, and the search for the man pictured in it, are our most intimate connection to the horror of that day."

And some salient mysteries:

Why don't we have answers to these 9/11 questions?