WTC 5 was a nine-story building that stood east of the North Tower (WTC 1). The building had two dozen tenants, with its fourth through ninth floors being occupied almost entirely by Morgan Stanley, Credit Suisse First Boston, and government agencies.

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Apparently the evacuation of Building 5 began shortly after the North Tower was hit. The South Tower crash deposited some remains of Flight 175's hull on the roof of WTC 5, according to FEMA's Report.
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WTC 5 was severely damaged by fallout from the destruction of the Towers. Large falling pieces of steel from the Towers' perimeter walls are the probable cause of the holes in the roof seen from above.
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Serious fires raged through WTC 5 for hours. Despite the massive structural damage shown by the holes, and fires far more severe than those in WTC 1, 2, and 7, WTC 5 did not collapse.
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WTC 5 was demolished as part of the clean-up of Ground Zero.