A New York man pleaded guilty to charges of mailing 21 death-threat letters laced with white powder to schools, U.S. officials and lawmakers between 1997 and 2012, according to The Associated Press (AP). Brian Daniel Norton reportedly pleaded guilty to two federal counts of conveying false information and hoaxes, according to a statement from the U.S. Attorney for the Northern District of New York.

Federal prosecutors say that Norton claimed the white powder was either ricin or anthrax. "In court, Norton admitted he mailed more than 20 death threat letters that contained a white powder he claimed to be either anthrax or ricin," the statement said.  The powder was reportedly harmless, according to AP. 

Norton will be sentenced on April 10 in Utica and faces a maximum of five years in prison and a $250,000 fine, media reports said.

The 59-year-old from Cicero also reportedly wrote messages on the letters. On one alumni donation card, he wrote: "Praise Allah for Sept. 11. You are next," , Reuters reported, citing local media, adding that the letters were sent to Bishop Ludden High School and Le Moyne College, in Syracuse.

Norton also reportedly targeted officials including Arizona Senator John McCain, then-Secretary of Defense Robert Gates and former Congresswoman Ann Marie Buerkle.