On October 2, 2001 (three days before the first fatality from anthrax in the 2001 domestic US terrorism attacks), FBI Agent Gregory Leylegian called and asked Assaad to come in for questioning, which he did the next day. The FBI had received an anonymous letter, postmarked September 21, 2001, in which an alleged co-worker warned that Assaad might be planning a biological attack. The timing is noteworthy because anthrax-victim Robert Stevens was not admitted to a Florida hospital until October 2, and he was not diagnosed with anthrax until October 3. The first set of letters containing real anthrax were mailed on September 18.