Maybe [they squawked VFR] to not call attention to themselves for as long as they can.

To not call attention to themselves, terrorists would get a regular
squawk code, flight following, and all that stuff, as if they were
passing through or going to one of the airports on the other side of the
ring. Then, at the last minute, they turn the transponder off, dive
past redline towards the target, and deliver their message.

Ok, that's still five minutes in a 150, maybe long enough to decide to
tell the President that his ride is waiting.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.