The FBI arrested Sen. Maria Cantwell’s staffer Mike McHaney Friday after he arranged to meet and have sex with underage boy. According to a complaint filed in U.S. District Court in Washington, D.C., brought to our attention by The Smoking Gun, McHaney was online Friday afternoon when a witness working with investigators asked if McHaney was interested in engaging in anal sex with a 13-year-old boy. “I’ll be there,” McHaney responded. McHaney was later arrested at a predetermined location where he had arranged to meet the witness. Until his arrest Friday, McHaney had worked for Democratic Senator Maria Cantwell. As of Monday night, calls to Sen. Cantwell’s office were not returned. Court documents after the jump.