In a 1983 documentary called Building the World Trade Center and produced by the Port Authority itself, a famous waltz begins at almost exactly the 9:11 minute mark. Most people will remember hearing this melody (very recognizable and famous) ... What is shocking is the name of the piece: the Vienna Blood Waltz by Johann Strauss. Any bit of music could have been laid behind this footage in the film, but this particular composition was chosen.
Go to 9:11 minutes:
Find the same notes beginning at 1:37 time code: