Re: Subterfuge runs deep, Sears Tower will still be bombed.
Personally, I think it was a "Red Cell" style of training operation to test the detection skills of the security forces there, but that doesn't mean it wasn't part of a later setup, either!
On a related sidelight, the Marion Intelligence Report of the year 1999 clearly alleges (per expert testimony) that the Russians "lost" about a hundred SC-115's, commonly known as "Suitcase Bombs" of the nuclear variety. This report also alleges that Russian cells in the US are actively cultivating drop points for these devices, one potential location being the Shenandoah Valley, just a stone's throw away from our nation's capital.
Why Russian? Because China and Russia had a plan a long time ago to tip the scale of global power away from the US and into their favor. The Russians are the ground forces, and the Chinese are the technology pirates.