Two and a half decades after the deadliest terror attack in modern history claimed almost 3,000 lives, the world is still haunted by September 11, 2001.As images of ash-covered survivors, the 'jumpers' facing an unthinkable fate, and heartbroken relatives continue to flash across our screens year after year, only those who witnessed the horror firsthand can truly convey what it was like that day.Thomas von Essen is one of those people. He was New York City's fire commissioner during the attacks and lost 343 firefighters who sacrificed their lives to save those trapped inside the burning Twin Towers that fateful Tuesday morning.Speaking to the Daily Mail, von Essen, now 80, has shared his heartbreaking memories of the attacks and issued a stark warning to governments today, saying they must remember the lessons of September 11 and ensure the conditions that allowed such an atrocity to happen are never allowed to take hold again.When Essen arrived to work on what he describes as a 'beautiful, clear day', in September, he could never have imagined what would unfold in the coming hours.'I got a report that a small plane had hit the North Tower of the World Trade Center. I could see it [from where I was] actually, and I said, "Oh, it looks like a lot of smoke."''I figured it was some rich guy who got drunk or whatever and crashed into the building,' he said.He rushed to the scene as fast as he could. 'I got there very quickly. The windows were already blown out on the ground, and I was walking through one of the windows, when about 15 feet away from me, I heard this horrible thud. Smoke billows from one of the towers of the World Trade Center as flames and debris explode Thomas von Essen (L) with New York Police Commissioner Bernard Kerik (C), Mayor Rudy Giuliani (C) and President George W Bush (R) in the days following 9/11 People run from the collapse of World Trade Center on September 11, 2001'I looked, and it was a person who had fallen or jumped from the sky.'He didn't know it at the time, but this was one of an estimated 200 to 300 'jumpers' who would, over the course of the morning, make the heartbreaking choice to end their lives rather than suffocate to death on the upper floors of the World Trade Center. 'When I got in the lobby, my fire chiefs said, "It wasn't a small plane, boss, it was a commercial jet."'The former fire commissioner recounted the horrifying moment they realised the extensive damage to the building, and that the water lines had all been severed.'We weren't going to be able to put the fire out. We were doing the best we could to evacuate people. But we knew that those above the 90th floor were going to die.'Then, at 9:03am, the South Tower was hit. 'We felt this big vibration - we thought it was an explosion in the elevator shaft. 'Someone walked in, and they yelled, "Commissioner, the South Tower was hit."'When the second plane hit, of course, that's when everybody thought: "Oh my God, we're being attacked, we're at war."'Von Essen quickly realised that the scale of the disaster was beyond the capabilities of the fire department, but his firefighters immediately began working to evacuate those trapped inside the towers. Thanks to the bravery of the FDNY, an estimated 15,000 to 18,000 people were able to escape the burning buildings that day. 'We did the best we could to coordinate everything, but the rest of the day just got worse and worse as we started to find out how many people we lost,' von Essen recounted.Following a previous 1993 bombing, emergency plans called for people to remain in one tower if the other was attacked. So when the North Tower was struck, those inside the South Tower were initially told to stay where they were. More than two decades later, von Essen still carries the weight of that decision.'If everybody had been evacuated immediately from the South Tower, we wouldn't have lost anybody. But did we know another jet plane was gonna hit the South Tower? Of course not.' Von Essen lost 343 of his men at Ground Zero that day. In the aftermath, emergency crews spent days combing through the wreckage, desperately searching for survivors buried beneath the rubble. A person falls head first from the north tower of New York's World Trade Center Thomas Von Essen (L) at a press conference alongside Mayor Rudy Giuliani (C) and Police Comissioner Bernard Kerik (R) in November 2001 People make their way through a cloud of caustic dust while fleeing Ground Zero on 9/11'I thought maybe there would be a piece of steel and a piece of concrete, and some young, innocent woman or man would be under there, breathing with a little bit of water dropping, and they'd survive for a few days, and we'd get them out. But we had no survivors after the first day.'Von Essen recounted the hellish weeks that followed, attending the funerals of close colleagues while struggling to cope with his own grief and despair.'To be the commissioner that lost more people than anybody ever before him was exceptionally painful for someone like me. It wasn't just a job, it was - then, and still today - very personal.'Going to the funerals and seeing a young woman in the first row of the church with a couple of kids sitting next to her, or a mother and father sitting there who had lost their son... it was horrible, I can't even describe it.'We couldn't even give [families] the remains. And you think things are bad, but then when you can't even give somebody the remains of their loved one, you realise, it could be worse.'Von Essen, who still tears up at the mention of his fallen colleagues, now has strong words for politicians he believes are allowing a climate of mass migration and rising extremism to take hold in their countries. 'I think we're really stupid, to a degree which is hard for me to believe. I think our politicians are nauseating. I think they should all be arrested.'Referring to the 19 Al-Qaeda terrorists who carried out the 9/11 attacks, he said: 'Letting 19 lowlifes into your country - that mistake I can understand.'But how you could let thousands and thousands of people into your country and not know who they are or what their mission is... I don't care what your politics are, I think that's idiotic.''I see what's going on in Great Britain. I think you guys might be as dumb as we are, … to not know the people who hate you, where they are, and what they are doing. Why you let them in to begin with, I don't get it.'Von Essen said these developments make him more concerned by the threat of terrorism now than he was before the events of 9/11. Von Essen, who still tears up at the mention of his fallen colleagues, now has strong words for politicians he believes are allowing a climate of mass migration and rising extremism to take hold in their countries New York City firefighters work at the World Trade Center in the aftermath of 9/11 People evacuate the World Trade Center on September 11, 2001'With all the improvements we have in technology and monitoring, the FBI, the CIA, everybody does a better job today of finding bad people and mitigating that. 'But I never thought that the bad guys would also have all this technology. They have AI, they're recruiting better than they did and getting more people.'They're morons, most of them, but they have intelligent leaders, and the intelligent people are playing the morons. So it makes it more dangerous than it was years ago.'The former fire chief, who worked closely with then-Mayor Rudy Giuliani in the aftermath of 9/11, also has some thoughts for New York's current leader.Zohran Mamdani recently came under fire online after a 2023 tweet resurfaced in which he referenced the deaths and suffering caused by the wars that followed the attacks, while notably failing to mention who carried them out.The mayor also faced backlash after appearing on an interview with online streamer Hasan Piker, who said in 2019 that 'America deserved 9/11'.More recently, Mamdani sparked further outrage among 9/11 survivors and their families after he was filmed signing an executive order designating a day of remembrance for the attacks, before handing the pen he used to sign it to a former Al-Qaeda defence lawyer.Following public outcry, a petition was launched urging Mamdani's exclusion from New York's annual 9/11 remembrance event. It has over 100,000 signatures.'I saw [Mamdani] hand a pen for a bill he signed about September 11th, to a lawyer for the [9/11] terrorists, and I thought, doesn't he get the visuals of that? Doesn't he realize this is the week of September 11th?,' von Essen said.'I don't know where he's coming from. For a smart man, seems pretty dopey to me, and I think if he was a big man, he wouldn't go to the ceremony on September 11th.'Post September 11, von Essen has dedicated his life to helping those in disaster zones.'I had this desire to continue. I worked for FEMA recently and was able to help with the hurricanes in Puerto Rico and the Virgin Islands, and the COVID response in New York City, so I'm still involved and still working and trying to help people.'He has also stressed the importance of educating children and young people on the attacks, working closely with UK-based charity Since 9/11 that aims to make education on the topic mandatory in British schools.'It's pretty relevant for kids to understand that there are bad people out there. They didn't go away. I think it's critical to the future for education on this topic to continue.'Von Essen was appointed an honorary CBE (Commander of the British Empire) by Queen Elizabeth II in 2002 alongside Police Commissioner Bernard Kerik and Mayor Giuliani in recognition of their outstanding service, resilience, and bravery in the wake of the attacks.Do you have a story? Email eliana.silvergokun@dailymail.co.uk