U.S. Attorney Jose Angel Moreno says Williamson -- warned earlier not to threaten government employees -- sent an e-mail in June 2008 from the Houston public library to the U.S. Attorney's Houston office threatening to blow up FBI headquarters, CIA headquarters and the Justice Department.
Moreno says Williamson also threatened FBI agents in a message sent from a Nevada library.
Williamson, arrested in July 2008 outside FBI headquarters in Washington, D.C., faces up to five years in prison. Sentencing is set for June.
