Federal agents on Wednesday arrested a suspect in the mailing of letters to President Barack Obama and a U.S. senator that initially tested positive for the poison ricin.The suspect was identified as Paul Kevin Curtis of Tupelo, Miss., federal officials told NBC News. They said he may appear in court as early as Wednesday night.Both letters carried an identical closing statement, according to an FBI bulletin obtained by NBC News on Wednesday.According to the FBI bulletin, both letters, postmarked April 8, 2013 out of Memphis, Tenn., included an identical phrase, “to see a wrong and not expose it, is to become a silent partner to its continuance.”In addition, both letters are signed: “I am KC and I approve this message.”