Los Angeles ? A man was arrested and accused of mailing threatening letters laced with white powder to Democratic leader Nancy Pelosi, David Letterman, Jon Stewart and other high-profile figures, the FBI announced Sunday.

FBI agents took Chad Conrad Castagana, 39, into custody Saturday on charges of conveying false information and sending threats via the U.S. mail, the bureau said in a statement.

Castagana, of Los Angeles, was being held in a federal detention center pending an initial court appearance today, when prosecutors were expected to file charges.

Some letters included phrases like “Death to Demagogues” and pictures of victims of the 2004 Asian tsunami, authorities said.

While the FBI is still trying to identify the white powder, preliminary tests revealed it does not pose a biological hazard.