Why did [they] choose 9/11 as a murder ritual date?
Because it hides the murderers birthdate.
ghwb born on day 164 of a leap year.
164 -5 code
1 becomes 6
6 becomes 1
4 becomes 9
619 -365 = 254
9/11 is day 254 of the year.
Too many coincidences, Captain.