MURRAY WEISS, NY POST: Threatening letters mailed to the media before the World Trade Center attacks - bearing striking similarities to the current anthrax-tainted letters - were mailed from Indianapolis, where the deadly bacteria was discovered yesterday, The Post has learned. The pre-Sept. 11 letters were addressed in block letters that virtually match the lettering on the anthrax-laced missives sent to Sen. Thomas Daschle, the New York Post and NBC, law-enforcement sources said. One source allowed The Post to see copies of envelopes from several of the earlier letters. Each line of the printed address clearly sloped downward to the right and the handwriting eerily resembled that on the anthrax letters. Federal investigators checked the return addresses on the letters, the sources said, but none of them was real . . . The similarities between the pre-Sept. 11 and post-Twin Tower disaster letters has further fueled a theory at the FBI and Justice Department that the anthrax scare is the work of a twisted home-grown menace rather than a terrorist linked to state-sponsored action or Osama bin Laden. Source say investigators are eyeing a number of groups, including radical members of a pagan cult.