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1.16.4.8 Examination of Explosive Residue Examination of recovered wreckage revealed trace amounts of explosive residue on three samples of material from three separate locations in the airplane wreckage. These material samples were submitted to the FBI s laboratory in Washington, D.C., with many other material samples for analysis. The pieces on which these traces were found were described by the FBI as a piece of canvas like material and two pieces of floor panel;however, the exact locations of the traces were not documented. According to the FBIís laboratory report,219 analysis of each of the three material samples revealed that they contained traces of different explosives: one contained cyclotrimethylenetrinitramine(RDX), one contained nitroglycerin, and one contained a combination of RDX and pentaerythritol tetranitrate (PETN). Subsequent investigation revealed that the accident airplane had been used for a dog-training explosive detection exercise at St. Louis-Lambert International Airport(STL), St. Louis, Missouri, on June 10, 1996. During that exercise, an airport police officer placed five training aids containing explosives (one of which was cracked and could have released small amounts of explosives) in various locations inside the passenger cabin. Training aids were placed in the following locations: (1) in row 1, in the center armrest compartment separating seats 1 and 2; (2) in a small closet at the rear of the upper deck; (3) in row 10, inside the rear pouch of the seat back in front of seat 9; (4) in row 20,in the overhead compartment above seats 1 and 2; and (5) beside exit door R3 (see figure 20 in section 1.6.3.2 for an airplane diagram).2201.16.4.8.1 FAA Studies on the Effects of Sea Water on Explosive Residue Contamination FAA personnel at the FAA ís William J. Hughes Technical Center in Atlantic City,New Jersey, conducted tests to study the effects of sea water on cloth and aluminum airplane parts that had been exposed to explosives contamination.221 Pieces of aluminum from the wing of a commercial airplane and pieces of airplane seat covers were contaminated with explosive residue by manually deposited explosives and by exposure to an actual explosion and were then immersed in sea water. In both cases, when the cloth and aluminum airplane parts were examined after 2 days of immersion in sea water, the explosive residues were completely dissipated. The FAAís report concluded, ìour experiments have shown that their [sic] is very little likelihood that blast deposited explosive materials remain very long on cloth or aluminum aircraft parts after immersion in [sea water].î The FAA attributed this, in part, to the explosive residues being ìsomewhat soluble in [sea water].î

Even if the trigger for the slab failure was identified, experts say, it still does not explain why the structure on top of it subsequently came down. Lehman said a question for investigators remains: “How could we have saved the rest of the building from collapsing.”

On February 16, 2020 Lloyd D. Nabors Demolition used 300 pounds of dynamite to demolish the building to make room for a $2.5 billion mixed-use project by De La Vega Development for that property.[4] The entire building collapsed except the core which housed the elevator shaft and stairwell. The core collapsed slightly at its base then just stopped falling. The core ended up stabilizing with a slight lean. According to Artemio De La Vega, CEO of De La Vega Development, "The core settled into the basement probably, approximately...I'd say 35 to 40 feet down into the basement, which is basically what is holding the tower.

. It added the board was requesting bids to replace the tank, but the permit would take three to six months to secure. It wasn’t immediately clear if that work was ever completed.