About 1,200 people gathered at a hotel in Los Angeles over the weekend for what organisers billed as the largest conference on the plethora of conspiracy theories that see the 2001 attacks on Washington and New York as, at best, official negligence, and at worst an orchestrated US attempt to incite world war.
Alex Jones, a syndicated radio talkshow host, told a news conference: "There are so many prominent people who are incredibly well-respected who have stated that the evidence is overwhelming that 9/11 was an inside job.
"There are hundreds of smoking guns that people need to be made aware of."
He called for George Bush to be impeached and accused the mainstream media of being slow to cover the growing movement of 9/11 sceptics.
The 9/11 and the Neo-Con Agenda conference comprised two days of seminars, video presentations and talks by groups including Scholars for 9/11 Truth, infowars.com and an appearance by Charlie Sheen, the actor.
Motives and oil giants
Most are convinced that the US military command "stood down" on the day of the attack, that the hijackers were trained at American military bases, and that the World Trade Centre towers collapsed because of controlled explosions set before they were hit by two hijacked aircraft.
Suggested motives range from expected benefits for US arms and oil conglomerates to revolutionary plans for a new world order headed by the United States.
There were calls for Bush to be
impeached over 9/11
The theories, derided by critics as wild and far-fetched, have mostly been confined to the internet, talk radio and the alternative press.
But a Zogby opinion poll in August 2004 indicated that 49% of those living in New York City believed that US leaders knew in advance of the attacks and failed to act.
The official 9/11 Commission, set up in 2002, cited government intelligence lapses in the failure to prevent the attacks by al-Qaeda that killed about 3,000 people.
A 10,000-page investigation by the National Institute of Standards and Technology held that jet-fuel fires weakened the structure of the towers and led to their collapse.
'War of civilisations'
Sheen, star of the TV sitcom Two and a Half Men, provoked a media storm in March by calling in interviews for an independent investigation.
"There are so many prominent people who are incredibly well-respected who have stated that the evidence is overwhelming that 9/11 was an inside job"
radio talkshow host
Webster Tarpley, author of 911 Synthetic Terror; Made in USA, said the attacks were an example of "state-sponsored, false-flag terrorism" designed by rogue CIA elements "to start the war of civilisations".
Tarpley said Washington was "gripped by war psychosis" and had used terror as a pretext to turn the United States into a police state.