Los Angeles ? A man was indicted Friday on charges that he sent more than a dozen threatening letters laced with white powder to celebrities, politicians and other high-profile figures.

Chad Conrad Castagana, 39, was being held in federal custody in lieu of $350,000 bail, authorities said.

Prosecutors allege Conrad sent letters bearing fake return addresses to Democratic Rep. Nancy Pelosi, of California; comedians Jon Stewart and David Letterman; Democratic Sen. Charles Schumer, of New York; MSNBC host Keith Olbermann; and Viacom Inc. Chairman Sumner Redstone.

The powder in the letters was harmless, authorities have said.

Castagana was charged with 14 federal counts of threats and hoaxes, one for each letter he is accused of sending. Each count carries a five-year sentence.