A new book raises doubts about a 1979 congressional probe that concluded President John F. Kennedy's assassination 50 years ago was the result of an undefined conspiracy. The book, "The Kennedy Half Century" by prominent political science professor Larry Sabato of the University of Virginia, questions the conclusion by the House of Representatives Select Committee on Assassinations that a shot was fired at Kennedy from the so-called "grassy knoll" on November 22, 1963, in Dallas.