9/11 remembered: Ruthless Osama fanatics began detailed hijack planning in 1999

Most came from Saudi Arabia, though there were individuals from Lebanon and the United Arab Emirates. Their leader in the US was Egyptian-born Mohamed Atta, 33, who flew the first airliner the terrorists crashed that day. Atta was the oldest of the hijackers, a former town planner who had led a terrorist cell whilst studying in Hamburg in the 1990s. The ages of the other 18 spanned 22 to 29.

Detailed planning for the attacks went back to at least 1999. The hijackers would be split into two groups – pilots to fly the captured planes, and what were termed “muscle hijackers” by the FBI, their job to murder passengers and crew to terrify the rest of the people on board into submission.

The first hijackers to arrive in the US were Khalid-al-Mihdar and Nawaf al-Hazmi, who settled in the San Diego area in January 2000.

They were followed by three who would become pilots of the hijacked plans – Atta, Marwan al-Shehhi and Ziad Jarrah, early in the summer of that year.

The fourth hijacker pilot, Hani Hanjour, arrived in San Diego in December 2000. The remaining “muscle hijackers” arrived during spring and summer in 2001.

Bin Laden regarded al-Mihdar and al-Hazmi as expert fighters. Both had trained at terrorist camps in Afghanistan and fought in Bosnia. Both obtained US visas in April 1999, and late that year visited Pakistan for lessons in Western culture and travel to help them avoid arousing suspicion in the US.

Those earmarked as pilots enrolled on flying courses in southern Florida. It was later to emerge that they showed no interest in learning how to land, which struck at least one instructor as odd.

On the morning of September 11, they boarded four flights in Massachusetts, Washington and New Jersey. They managed to smuggle “box cutters” – craft knives – on board with them.

Aboard American Airlines Flight 11, after the hijacking, Atta was heard speaking over the air traffic control system, inadvertently broadcasting a message he intended for the passengers. “We have some planes. Just stay quiet and you’ll be OK. We are returning to the airport.

It was the most cynical of lies to keep passengers quiet. Aboard United Airlines Flight 93, Ziad Jarrah, 26, also broadcast to the passengers to keep them quiet. “Ladies and gentlemen, this is the captain. Please sit down. We have a bomb on board, so sit.”

This time, though, the passengers were not fooled. One of them, Tom Burnett, 38, had called his wife on a mobile phone to tell her that the flight had been hijacked. By then, she was able to tell him that the first three hijacked airliners had crashed. Mr Burnett and his fellow passengers resolved to fight back. At 9.57am, the cockpit voice recorder taped the sounds of crashes and screams. A voice could be heard shouting, “Let’s get them”. Four minutes later, United 93 nosedived into a field.