Completely unfounded. The US has this too huge and poorly researched watchlist, and they thought several people who were on it were on these flights, but the French questioned and cleared them all. And the only reason they mentioned Las Vegas was because it was on the flight path of a Paris to L.A. plane, but it is complete guesswork on their part; extrapolating blindly from a premise that turned out to be untrue in the first place.
The goverment may or may not have had valid reasons for their own hyping of this, but once the media got ahold of it they blew it all out of proportion like they always do. Here is a tip, always look at everything American news does, particularly broadcast news, with the awarness that they want people to tune in as much and as often as they can, and that causing fear and panic about something so you will came back soon for an update is a common practice for them, and that they never want anybody to tune out because they are bored with in depth coverage or they are showing too many important but tedious stories instead of the mindless pop fluff that people want to see. Keep all that in mind and you can begin to put American broadcast news in its proper place.
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Ninti - MK IIa 60GB Smoke, 30GB, 10GB