A New York state inmate has been charged with mailing hoax anthrax letters to five U.S. District courthouses in Virginia, New York and Washington, D.C., in 2007.

Robert Cepeda pleaded not guilty Thursday to sending letters from Auburn prison that federal prosecutors say contained harmless substances and warning letters.

The letters were addressed to District Court clerk's offices in nearby Syracuse, Washington and three Virginia cities -- Charlottesville, Harrisonburg and Alexandria.

An FBI investigator says the letters were not intercepted at Auburn prison and reached their intended destinations.

The messages variously stated that "This is ANTHRAX," "ANTHRAX for you" or "Die from ANTHRAX."

The 46-year-old was sentenced in 2006 to 4 years to nine years for ID theft, burglary and attempted placement of a false bomb.