This "unpleasant substance" is new to me -- thanks for the information. I assume he said this on his radio or TV show? I don't think the two articles I saw mentioned this. Did he give any other information that wasn't in the published articles?
I figure that the letters must have been striking, well beyond the ordinary crank letters that celebrities frequently receive. If not, Hannity wouldn't have remembered them so well as to have been immediately struck by the similarity when he saw the photos of the actual anthrax letters.
As for why he hasn't mentioned them further, maybe he's been told it would impede the investigation (although it probably wouldn't -- and the FBI has released pictures of the real anthrax letters, so I don't know whey they'd be more secretive with these). Maybe Hannity just wants to steer clear of terrorists and other murderers; this would certainly be sensible in terms of his own safety and that of his family. But why isn't the FBI bringing this out, and why isn't some enterprising reporter looking into it?
When journalists are directly involved, as in this case, you'd think that there would be so much scuttlebutt among reporters that nothing could be kept secret for long.
I got the impression he would have said nothing at all
had there not been some news reports
which mentioned that Fox/Hannity had received these letters.
I believe he suggested that the unpleasant substance
was excrement.