Earth, Wind & Fire song: What really happened on the 21st night of September?

NEW ORLEANS-- So you know the song, "September" by Earth, Wind & Fire.  Well, in that song, there's a popular line that goes:
"Do you remember the 21st night of September?"

News with a Twist Reporter Kenny Lopez got to thinking what really happened on the 21st night of September to get Earth, Wind & Fire to use that specific date in their hit song.   Kenny went around the WGNO newsroom and asked what our news staff thought the answer to the question is!  Hey Earth, Wind, & Fire if you're listening, please tell us the significance of September 21st!