It was a Friday.
September 11th can be on any day of the week
It was a Tuesday.
Sunday
September 11 2001 was a Tuesday.
Sept. 11, 1930 was on a Thursday.
The 11th of September 1958 was a Thursday.
September 11th, 2003 fell on a Thursday.
June, 11, 2009, was a Thursday.
April 11, 2009 fell on a Saturday.
September 11, 2009 fell on a Friday.
Saturday!
Wednesday