It's certainly possible and there would have been reason to shoot it down and cover it up. I wonder if we will ever know.
Do you believe it's possible that they 100% lied about one of the planes, but told 100% of the truth on the other 3 planes?
And, seeing as there was no debris at the Pentagon site (well, enough to fit in the back of a pickup truck), and if you believe they lied about plane #4... Don't you start to scratch your head on plane #3?
If you find a used condom in your living room and your GF admits to fcking the mailman...
But she completely denies knowing anything about the used condom in your bed...
Do you still trust the bitch?