The thing that really bothers me is, these threats were presented to the Govt. YEARS ago and NOBODY listened. As far as the media is concerned, they are far to quick to release news that is either false of case sensitive. On one hand, I think another attack is a given. The repetition of the information helps us prepare mentally for the unthinkable. Just as much a factor- sensationalism sells. It was reported that CNN sent a note to their advertisers a day or so after the bombings that went something like- look at our ratings-stick with us.
They (chemists and biologists) say bio/chem weapons are difficult to handle and dispense, but Fox
http://www.foxnews.com/story/0,2933,34409,00.html has an article on how they trained people to mix chemicals with oils and put it on DOOR KNOBS or feed it into air intake vents. We really need to clean out the US as best we can before we launch an attack. Hopefully, we can mute anything similar to WTC.
I can think of a million things that are more plausable and just as deadly.