I had just returned from Saudi Arabia as a US diplomat when al-Qaeda struck. We must remember who did it

The chargé d'affaires and I reported this conversation to the State Department the next day, but we received no comments back. In internal discussions at the embassy, we reviewed multiple threat reports, but many appeared to be made-up or far-fetched. We thought a major attack was coming, but most likely somewhere in the Middle East.

I had only been in my new assignment at the State Department for a few weeks on the morning of September 11, 2001. Just before the morning staff meeting, my office director and I watched the television report of the first plane hitting the North Tower at 8:46 am. It seemed impossible and my first reaction was that it likely was some kind of freak accident. When the second plane hit the South Tower about a quarter of an hour later, we all understood it was deliberate and most likely a terrorist attack.

I went to the secure section of the Near East Bureau to review intelligence reports and suddenly felt the windows vibrate. Looking up, I saw the Pentagon, less than two miles away across the Potomac River, partially in flames. Assistant Secretary Bill Burns convened an emergency action meeting in the bureau’s conference room, but almost as soon as we had gathered, we received instructions to evacuate the building.

Many of us gathered outside the C Street entrance as rumors circulated, first that other targets had been struck in Washington, including the White House, the Capitol building, and the State Department in front of which we were standing. Then we learned that the fourth plane had crashed in Pennsylvania. We did not know yet of the heroic passengers and crew who forced the hijackers to crash. State Department security soon ordered everyone to go home, monitor the news, and take shelter. No one knew whether more planes were on the way.

I went off in search of my partner at the time, but couldn’t find her, I tried calling but cell phones weren’t working. Twenty-Third Street Northwest, located on the west side of the Harry S. Truman building, leads to the closest Metro station and it was packed with government employees trying to find a way home. I recall a lot of confusion and anger, but not panic.

We were living in an apartment in Arlington, Virginia, just a few miles south of the Pentagon. I managed to board the Metro, headed toward Arlington, but there were warning announcements that the Metro could only run as far as Rosslyn, the closest stop in Virginia, since the Pentagon station was closed, blocking the rest of the line. I got off the Metro at the Rosslyn stop and boarded a bus headed in the direction of the apartment.

There were emergency vehicles everywhere, many of the main roads were closed, and when I realised that the bus could not enter the highway, I decided to get off and walk. As I reached the pedestrian bridge across I-395, I looked down the highway and could see that the western facade of the massive Pentagon building was blown apart, with flames still shooting into the air. I walked to the apartment and turned on the TV in time to watch the World Trade Center North Tower collapse. On the TV, I could see streams of New Yorkers in the streets, covered in ash and many with bloody faces, determinedly walking uptown, away from the horror that had struck Lower Manhattan.

The United States had just suffered the largest and most extensively planned terrorist attack in history. It wasn’t confirmed yet who had done it, but coming from Riyadh, I had no doubt it was Osama bin Laden and al-Qaeda. Something fundamental had changed. Al-Qaeda had demonstrated how non-state actors could carry out trans-national attacks on a massive scale. I also understood that the United States would soon unsheathe its “terrible swift sword,” with repercussions that would last for years to come.

That night I volunteered to work the midnight shift with the State Department’s emergency response team in the Operations Center. I was touched by the outpouring of support offered from governments all over the world, even if most of it was not deemed to be practical.

Then, we all went back to work. The flames at the Pentagon were put out, the bodies removed and buried with honour. One hundred eighty-four people died in the attack on the Pentagon and over 100 more were injured. In bed in Arlington in the early morning hours, I could hear low-level overflights of fighter jets on patrol over Washington. We read the early reports confirming al-Qaeda’s responsibility and later watched on television as President Bush delivered an ultimatum to the Taliban’s Mullah Omar, demanding that he hand over Bin Laden or face the consequences.

I was fully supportive when President Bush announced that we had invaded Afghanistan, and was startled to see university students at George Washington University handing out leaflets defending the Taliban and protesting the war. I remember a nervous and anxious America, but also spontaneous displays of patriotism and national unity. Those involved in the early days of the Global War on Terror shared a fierce determination to seek and destroy everyone who had done this to us, thus ensuring they could not do it again. In a display of unity almost unimaginable today, both Houses of the US Congress voted almost unanimously to authorise the use of force against those involved in the 9/11 attacks.

Twenty-five years later, that unity is gone. Bin Laden is dead and al-Qaeda largely destroyed, but many young Americans declared themselves fascinated by Bin Laden’s Letter to America, his justification for 9/11, when it recirculated recently on social media. Last week I read Douglas Murray’s essay in The Free Press describing the impact of online conspiracy theories on a new generation that may not even remember 9/11 and is dangerously inclined to accept outlandish accusations backed up by nothing but a generalised suspicion of our government.

I’m shocked that seemingly serious politicians and commentators in today’s America are willing to dismiss the threat of extreme Islamism or even seek the support of radical influencers such as Hasan Piker who claimed that “America deserved 9/11.” Near my former home in Maryland, I was stunned already some years ago to see a parked car with a bumper sticker reading, “9/11 was an inside job.”

In the months that followed, residents of Greater Washington lived through a series of bizarre incidents including cases of anthrax sent through the mail (still unsolved), the DC sniper duo (arrested and tried, one of them executed by lethal injection, the other in prison), who shot and killed ten random strangers going about their daily routine over a three week period in 2002, the strange atmosphere of anxious vulnerability mixed with a righteous desire for justice.

We who remember must raise our voices now and affirm: Bin Laden did this, it came out of a specific Islamist ideological and religious milieu that was centred in Saudi Arabia, Afghanistan, Sudan, Yemen and Pakistan, we know this and it is not open for debate.

By all means let us argue about the means that were used in the War on Terror, the wars in Afghanistan and Iraq that came next and how they ended. But let us not neglect our obligation to appreciate those who fought and sometimes died to ensure there would be no second 9/11, while continuing to share our experience with the new generation who may believe in unfounded conspiracy theories.

The fact is we do know who did this and how they did it. We must not forget and must not remain silent.

Marc Sievers is a former US Ambassador to Oman and a senior American diplomat with over three decades of experience in Middle East affairs. He later served as the founding Director of the American Jewish Committee’s Abu Dhabi office