A good read on the plot against JFK (apparently the terros weren't sure whether the were hitting the place or the man):

http://www.schneier.com/blog/archives/2007/06/portrait_of_the.html

In the case of Russell Defreitas, of course exploding kerosene tanks would cause some issues; but the majority of media emphasises were on the "unthinkable effect" of blowing pipeline burried under NY crowded areas. That would be if Russell Defreitas was a total genius and discovered a way to detonate kerosene without any need for oxygen as the pipe are... burried (and I'm not a NY soil specialist but I don't think the city is build on thin air).

Oh my gosh ! Are we going to have to invade it again ?

As for New York, it's not built on thin air, it's built on hot air. ;-)

Yes, and you'll have to invade again and again until you get it right!

... would a fart be classified as a biological weapon?