[aculeus]

Clue #1: in the rest of the world including the middle east, the tragic date was 11-9.

Clue #2. Despite Clue #1 because the letters were mailed in the USA it is probable the sender was in the USA and was familiar with the American dating convention.

[is_is]

what am i missing....either way....9/11 or 11/9 it's the same day of the year....Sept. 11 ????

[tbeatty]

Ahh yes, bad grammar is a clear clue to his foreignness but American colloquial expressions show his sophistication. You're a regular Sherlock. Almost like the answer is more important than the evidence. hmmmm.