Perhaps the fires weren't providing enough shock and awe to warrant a dozen year war in retribution?
NWO Garden Gnome #1: The plan is we're going to attack the Pentagon with a cruise missile disguised as a plane.
NWO Garden Gnome #2: Why?
NWOGG#1: It'll horrify people to think that a passenger jet full of random people was crashed into the headquarters of the US military. They'll give us carte blanche to invade Iraq and take their oil.
NWOGG#2: So we'll do it in the evening, then?
NWOGG#1: No, broad daylight in front of God and everybody. It'll be awesome.
NWOGG#2: Seems okay so far. What about debris? A jet airliner weighs, what, over 300,000 pounds?
NWOGG#1: That's okay, we'll just have the FCC investigators bring a couple of truckloads of scraps with them and spread them on the lawn. The reporters and first responders shouldn't notice that they're taking stuff out of a van and putting it down instead of picking it up. They're pretty stupid.
NWOGG#2: Right you are. What about other damage? Can we have someone saw down a couple of light poles and claim they were clipped by the plane?
NWOGG#1: Oh, that's terrific! The little details make all the difference, just like the jet-engine-cannon we're going to install in WTC 1. I think we can get a random taxi to drop a pole onto, you know, to make it look authentic. Again, nobody will notice this preparation out in the open, in broad daylight. As I said, people are pretty stupid.
NWOGG#2: This seems pretty terrifiying, what with the random threat of hijacking and all. We're going to spread these out through the week, right?
NWOGG#1: Oh, no. We'll do it all on the same morning. We're blaming this on al quaeda. They always do those simultaneous suicide attacks, like the African embassy bombings we faked a few years ago.
NWOGG#2: We did those? Wow. I thought those were the real deal.
NWOGG#1: Nope. Al quaeda always screws these things up so we stopped paying them and started doing it ourselves.
NWOGG#2: I like it so far. But I think we need something more. I know a guy who has the world's largest disco fogger. We can borrow it and drive it into the wreckage to make smoke, tell everyone something was on fire. I dunno, a generator or something.
NWOGG#1: That's a good idea. How long will it run?
NWOGG#2: Only about 15 seconds. Should be enough for a few pictures. It won't really obscure what we're doing in the hole, though, so we're going to have to get the Pentagon librarians to carry airplane seats and dead bodies through the Pentagon and shove them into the rubble.
NWOGG#1: Won't people notice that stuff moving through the halls?
NWOGG#2: Have you ever been inside the Pentagon? That place is a maze. Nobody will notice we're going the wrong way.