A copy of the that letter and envelope doesn't exist, but there's no evidence that it was mailed to him (or anyone else) by name; there was testimony that a letter with powder was opened by a clerk and thrown in the trash. Stevens was contaminated by vacuuming spreading the dust around.
Minor point:
The best discussion of his exposure is by Leonard Coleman, a professor who interviewed the folks at AMI. He says that Stevens looked at a letter re JLo’s upcoming wedding. There was a powder and jewish star. He put it down on his keyboard (where a concentration was found). The contamination through the Post Offices, according to the CDC, suggests there were actually two letters.
Jenny was Atta and Ramzi’s code. Wedding was code for event.
But you are right the hijackers were dead and thus could not have mailed the anthrax. The 911 imam providing counsel to two key hijackers (Hani and Nawaf) was coordinating with the man whose lawyer says the FBI considers an anthrax weapons suspect. He was the main speaker for the only US charity promoted by Al Qaeda’s website (which was hosted in New Brunswick, NJ). He was convicted to life plus 70 years and his sentence has been remanded. He used to work for Andrew Card when he was secretary of transportation. His office was 15 feet from Ken Alibek and the former USAMRIID deputy commander. He had a high security clearance while at SRA at the same time as the former USAMRIID deputy commander.
Bottom line is that the fact that the hijackers were dead is the beginning of analysis, not the end.
http://www.anthraxandalqaeda.com
The FBI has been doing very well and the fact that they have been able to keep the public in the dark is perhaps to their credit, perhaps not. It is difficult to tell presently. But we will see this year, I believe.