Authorities searched for years for the source of racially hateful letters, including one threatening to blow up the U.S. Supreme Court, before tracking him down when he started sending messages via e-mail instead of U.S. mail, authorities said.

The FBI said Thursday that letters dating to the late 1980s seemed to stop in the early 1990s but started again later that decade. Cleveland FBI agent Scott Wilson said agents never stopped looking for the writer, and he told The Plain Dealer newspaper that they found him a few months ago by tracing the e-mails to David Tuason’s account.