Ten million have watched so far, and that's only a fraction of the 42 percent of Americans recently polled by Reuters who believe its message — that our own government covered up critical evidence of 9/11, CBS News correspondent Jim Stewart reports.
But it's more than conspiracy theories on the Internet at work here. Some of the very people who first investigated 9/11 admit there's still a lot they don't know about the plot.
Dale Watson ran counterterrorism for the FBI and led the investigation into 9/11. And one of the things that still puzzles him most is the Las Vegas connection.
All four of the 9/11 hijacker pilots flew Las Vegas in the months preceding the attack. Some came twice. But once here, the men essentially disappeared.
Five years later, what does Watson think they were doing?
"That's still a mystery to me, and I do not know the answer to that to this day," Watson told Stewart.
What worries him is the possibility that the hijackers had help somewhere in the United States — operatives who could still be here awaiting further orders.
"Were there other people checked in there, that were planning something else?" Watson asked.
Watson doesn't think they missed anyone, but Las Vegas Undersheriff Doug Gillespie, who was part of the original investigative team, says he's not certain.
"We're not sure why they chose Las Vegas," Gillespie said. "There's a lot of surveillance cameras inside hotel casino properties that have gaming."
But did they ever find any pictures of the alleged terrorists anywhere on any of them?
"No. None," Gillespie said.
A stripper at this club said she saw them. Police doubt it. They told a rental car company they were staying at this hotel, but they never showed.
And that's not all that continues to puzzle agents about the Las Vegas visits. On his first trip here hijacker Muhammad Atta rented a car, and drove it 110 miles in two days. But where did he go? Who did he visit with, if anyone?
There's not a clue.
And the loose ends aren't just in Las Vegas. Why did Muhammad Atta and his sidekick travel all the way to Portland, Maine, to connect with — and almost miss — the Boston flight they later hijacked? Fellow travelers remember how they stuck out.
"It was a little odd to see someone of Arab descent way up in Maine," Vincent Meisner said.
Why did Atta earlier travel all the way from Florida to Virginia Beach, Va., just to rent a mailbox? Some agents speculate he went there to scout the Atlantic fleet as a possible target. Others wonder if he had a secret meeting with a messenger from al Qaeda.
The FBI still doesn't know — but hasn't stopped looking.
Five years after the crime a dozen agents remain on the 9/11 case. And they still get 20 new leads a week.