It's a different kind of 9/11 commemoration: Ten years after four hijacked airplanes crashed and nearly 3,000 people died, activists are staging events across the country to denounce as lies the official accounts of what happened that tragic day.
The conspiracy allegations began flying even as firefighters were dousing the smoldering remains at Ground Zero -- and they endure a decade later despite investigations that have debunked them.
One group of so-called 9/11 "truthers" believes "controlled demolitions" brought down the two towers of the World Trade Center and an adjacent skyscraper.
There's the conspiracy theory that a cruise missile – and not a Boeing 757 – struck the Pentagon and that Flight 93 actually was shot down over western Pennsylvania. And there's the claim that U.S. air defenses were ordered to "stand down" on 9/11, allowing the hijacked airliners to hit their targets.
And that's just for starters.
"Whenever I am asked to speak about 9/11, it's rare that I speak without some of these theorists showing up. It's always the same people. They always ask the same questions -- and then we move onto the next meeting," said former N.J. Gov. Tom Kean, the co-chairman of the 9/11 Commission.
"They are not bad people … they just have these views that I cannot understand at all."
Rep. Peter King, R-N.Y., chairman of the House Homeland Security Committee, is less diplomatic, charging that conspiracy theorists "trivialize" the "most tragic event to affect the United States."
"People making these claims are disgraceful, and they should be ashamed of themselves," King said.
Most truthers believe that elements inside the U.S. government planned the 9/11 attacks or allowed them to happen, to justify the invasion of Iraq. And this week they are trying to use the tenth anniversary of the attacks to convince more Americans to rally around their cause.
The group We Are Change says it is sponsoring a 228-mile walk from the Pentagon to Ground Zero "to help bring attention to the ongoing coverup."
Leading truthers from around the world have assembled in Toronto for a four-day 9/11 "inquest." They will try to convince a panel that includes an Italian judge, an urban planner from the University of Tennessee and a Canadian professor of psychology that the Sept. 11 attacks really were the product of a conspiracy.
And the organization Architects and Engineers for 9/11 Truth is screening a new movie in the U.S. and Canada showcasing their claim that explosives brought down the Twin Towers and a 47-story building that collapsed later that day, 7 World Trade Center.
Talk of conspiracies crackled as an overflow crowd of more than 150 people crammed into a tiny theater in New York City's East Village on Wednesday night for the movie's premiere.
"And on the tenth anniversary of 9/11, there just happened to be Flight 93 footage that emerged," one member of the audience said sarcastically to another. He was referring to a never-before-seen video that surfaced this week of the smoke rising from the Flight 93 crash site.
"Yeah, who is going to conduct a new investigation – the same people who did the first!"
An organizer took the stage. "Ten years. It's been a long time. A lot of familiar faces here," he said.