I don't think it was staged at all. Let's be honest, it's relatively easy to disturb the peace.
Your post is my principal cause for suspicion that all these terrorist warnings and terrorist lists are government propaganda.
It would be all too easy for a sociopath or a Muslim terrorist to kill a large amount of people at some mall or some sporting event. The fact that this never happens, despite thousands of opportunities, tells me that our government is using this propaganda for their own purposes.
I think it is near impossible to bring an assault weapon into a major sports arena. MLB requires all stadiums to have metal detectors installed. NFL and all other leagues are doing the same. A lot of changes have been made since 9/11. Examples: Soldier Field don't allow bags into the stadium. Security guards at every entrance.
They wouldn't even bother with tightening security if the threat wasn't real.
We have already seen multiple mass shooting in malls. I don't know how you could say it never happens.
Terrorists like using explosives and those can be planted in advance of the sporting event.
The mass shootings are partially the result of patients being subscribed psychotropic drugs (we can't say gun laws because the malls almost always have a "no gun" policy).
Our government is using this propaganda to further their cause, by this I mean extending their own powers and limited ours. This is going to bite us hard in the future.
The list of terrorist suspects is almost a million or so people yet 9/11 was allegedly pulled off by 19. So, the math doesn't work here - if there were hundreds, or thousands, or tens of thousands of terrorists were running around planning things, it's a certainty that they would have at least a minimum of success and it's telling that they have not had any.
And look at the general philosophy of our government with it's "invade the world, invite the world" mentality. We have porous borders and an exuberant, on steroids military and we even operate drones in other countries.
So, in short, our government is probably lying about terrorists to expand their own powers.