Today marks the 12th anniversary of the September 11th attacks on the United States with ceremonies around the US and elsewhere, including here in Australia.
The legacy of the attacks still remains a strong influence in counter-terrorism and foreign policy in many Western countries.
Ildi Amon reports.
"Here comes another one, I'm taking a look. (Explosion ...) Ew! ... Oh, my God! ... There's another one! (Explosion ...) Oh, serious! (More explosions ...) Oh, my God! ... I saw it with my own eyes! It must be an attack or something ... Oh, my God! ... Another plane just went in ... The other tower!"
The horrors witnessed when the second United Airlines jetliner flew into the South Tower of the World Trade Centre in New York on September 11, 2001.
Almost three-thousand people died in the attacks on the World Trade Centre and the Pentagon, and in a plane crash in Virginia that day.
Among them was 29-year-old Adelaide man Andrew Knox.
Mr Knox had been working as an environmental architect on the 103rd floor of the World Trade Centre's North Tower when the first of four hijacked planes struck.
Mr Knox's twin brother Stuart says even years after the attacks, it's still hard to let go.
"You get the constant reminders. You obviously get them on the anniversary, but we get it from images that relate to any form of terrorism. You (also) have the images of the (World Trade Centre) buildings being hit. And I guess that that ... has been one of the hardest things, because of the fact that you're looking at the fact that, if a loved one died in a car crash, nobody's filmed it, nobody plays it for you repeatedly. But, for something like September 11, you have images of the, um ... of the time that your loved one was killed."
Andrew Knox was among 11 Australians who died in the attacks on September 11.
The United States, then led by George W. Bush, responded to the attacks by launching the so-called War on Terror.
The campaign saw the US invade Afghanistan to try depose the Taliban and shortly after led to the war in Iraq.
Then Australian Prime Minister John Howard, who was in the US at the time of the attacks, invoked the ANZUS Treaty and threw Australia's military support behind America.
Michael McKinley is a senior lecturer in international relations and strategy at the Australian National University.
He says the flow-on effects of 9/11 still dictate counter-terrorism policy in many Western countries.
"9/11 is basically the overall determining force of current counter-terrorism policy throughout the West, not just in Australia and the United States. It has had an extraordinary influence and it really has overshadowed all other events which required a reaction and all other events prior to 9/11. It is the force of policy."
Many of the measures introduced in response to the 9-11 attacks - for example new restrictions on what can be carried in hand luggage onto aircraft - remain in place.
