Why did Mohamed Atta and four other hijackers visit Las Vegas in the months leading up to the September 11 atrocities?
Was it to drink alcohol, chase women and order giant pizzas in a final hedonistic binge before their suicide missions, as some news reports have suggested?
Or was it to attend secret meetings in which the multiple strands of the plot to attack New York and Washington were pulled together?
Either way, Las Vegas is an important location in the conspiracy, as American investigators continue their efforts to identify associates of the 19 suicide hijackers and to prevent future atrocities.
The list of locations around the world on the trail of Atta, the alleged ringleader, and some of the men in his group is extensive: Florida, New Jersey, Spain, Germany, Prague, the Philippines and, on the eve of the attacks, Portland, Maine.
But Las Vegas is the only one to have attracted such a big crowd of them.
The hijackers, including all four presumed pilots, travelled to the desert city on six separate occasions between May and mid-August.
Atta, who smashed the first American Airlines plane into the World Trade Center and is known to have had contact with the other hijacking teams during his travels, visited twice, in late June and in mid-August.
His friend - and, according to some reports, cousin - Marwan al-Shehhi had preceded him in late May, followed within days by Ziad Jarrah.
Nawaf Alhazmi and Hani Hanjour were in Las Vegas in August, at the same time as Atta. At some point in the summer, there was also a visit from Lotfi Raissi, an Algerian pilot under arrest in Britain on suspicion that he helped teach some of the hijackers to fly.
The FBI in Las Vegas is tight-lipped about who may have met whom during these visits, and why.
It seems plausible that the city - cheap, well-connected by air and far from the proposed scene of the crime - would have been chosen as a secret meeting point. The trips to Las Vegas also confirmed a pattern of repeated air travel, reducing any possible suspicion over the multiple ticket purchases for September 11.
Some details of the Las Vegas trips have also been revealed.
The men stuck to two distinct areas of the city, one just north of the big resort casinos on the Strip and the other around the campus of the University of Nevada.
They appear to have stayed in one of two cheap hotels, the Royal and the Econo Lodge. According to the owner of the Royal, the FBI has asked questions only about Room 2, prompting speculation that it could have been used as a "safe" location for several people and material over an extended period.
Some of the men were also seen in a Starbucks cafe near the university. And Atta and Jarrah spent time in an internet cafe called Cyber Zone, where one of the most popular online games pits players against a ruthless gang of terrorists.
What Atta and the other hijackers got up to in their time off in Sin City has been a subject of considerable speculation. Some reports have spoken of girlfriends, drinking binges and more - all in apparent contradiction of the tenets of Islam.
One stripper at the Olympic Garden Topless Cabaret, not far from the two motels under scrutiny, swears she gave a lap dance to Marwan al-Shehhi in June and remembers him as uncommonly tight-fisted.
Her account fits with other descriptions, from locations as diverse as Florida and the Philippines, suggesting the hijackers enjoyed women and liquor but hated to part with any more money than they absolutely had to.
In the Philippines resort of Mabalacat, hotel workers remember al-Shehhi indulging in raucous whisky-drinking sessions with friends, and Atta entertaining different women in his room every night. Both were recalled as bad tippers.
Some investigators in Las Vegas are not so sure about the high-living, however, questioning the reliability of the stripper's memory after more than three months.
They believe the hijacking crew was more likely to have kept to itself: Las Vegas is a good place for people who don't want to be conspicuous.
Another part of the established pattern are the reports of pizza eating (an extravaganza from Hungry Howie's, without the ham, called "The Works") and cheap living.
That part of the Las Vegas experience fits in with a new account of the movements of Atta and another suspected hijacker, Abdulaziz Al-Omari, in Portland on the eve of the attacks.
Video surveillance footage released by the FBI shows the pair ate at Pizza Hut, spent 20 minutes in a Wal-Mart store, filled their rental car with petrol and slept at a discount hotel, the Comfort Inn.
That last night, all of it spent along a single stretch of Maine Mall Rd, could not have been a more comprehensive tour of the banality of strip-mall America.
It seems their aim was to blend in.
In video footage taken at a bank's cash machine, Al-Omari is grinning. Atta looks stony.
It is not clear why Atta took the pair to Portland on the eve of the hijackings, but the city's authorities hope the material, and a brief timeline of the two men's activities, will jog memories and yield further clues, possibly of a local contact or some connection maintained by the hijackers.
- INDEPENDENT
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