Terrorist voice recognition

Does anyone else find it odd that the tape of the 911 call, threatening the
terrorist bomb at the Olympic Park, still hasn't been released to the media?
It would seem that there is at least a possibility that someone could know
this person's voice and finger him for the feds...
I have a [disturbing, hence anonymous] explanation: The feds figure they have
already got a pool of people who can recognise the voice of a pipe-bomber, as
sworn courtroom admissions show that the previous pipebombs' burial locations,
supposedly known to "the Georgia Militia," were actually only known to a single
government informant infiltrator. [The media, for some strange reason, didn't
choose to report this little item. The militia case has now been delayed.]
Hmmmmmmmm.