WEST PALM BEACH, Fla. (AP) -- A Florida prison inmate has been sentenced to more than six additional years behind bars for sending a threatening hoax letter to prosecutors.

The sentence was imposed by a federal judge Friday on 28-year-old Justin Burton Lane. The federal sentence won't begin until Lane finishes the eight years he has remaining on burglary, robbery and theft convictions.

Federal prosecutors say Lane mailed the threat letter in January from state prison in Raiford to the offices of the Palm Beach County state attorney. The letter named then-State Attorney Michael McAuliffe and an assistant prosecutor and contained a white powder.

Hazardous materials teams later determined the powder was not harmful.

Lane previously pleaded guilty to two charges of mailing threats and hoaxes. He has a lengthy criminal record.