If I was planning it, I would have several events like this, get everyone on edge for the 4th, and then nothing. Wait until Labor Day or so and then . . . . . .
Hmmm - possibly. Wait until everybody relaxes and thinks nothing's going to happen, then they hit hard, maximizing the shock value.
Sort of like the Y2K terrorism fears that had a lot of people scared silly (although that cretin DID try to sneak into the U.S. through Canada to bomb LAX) then - 9/11.