Charles Julius Guiteau ( September 8 , 1841 â `` June 30 , 1882 ) was a lawyer and the man who assassinated the 20th President of the United States , James A. Garfield . Charles Julius Guiteau ( September 8 , 1841 â `` June 30 , 1882 ) was an American lawyer who assassinated U.S. President James A. Garfield on July 2 , 1881 .