NEW YORK (Reuters) - A man charged last year in a suspected Iranian-backed plot to kill the Saudi ambassador to Washington was expected to plead guilty on Wednesday to terrorism-related charges, a person familiar with the matter said. U.S. authorities accused Manssor Arbabsiar, 57, in October 2011 of being tapped by Iran's security agencies to assassinate Saudi Ambassador Adel al-Jubeir. Arbabsiar, who was arrested on September 29, 2011, when he arrived at John F. Kennedy International Airport from Mexico, is a naturalized U.S. citizen and holds an Iranian passport. ...