How the September 11 plot unfolded

The weapons were crude, the plot staggering in its conceit. Bring down buildings, kill, shake America to its core.

A year later the what-ifs - the myriad ways disaster might have been averted if only certain things had happened years ago, weeks earlier, minutes before - hang out there still, like the trails of smoke that took months to vanish from the fallen giants of New York.