Why is the Komitet Gosudarstvennoi Bezopastnosti is thrown into a panic when it hears that the assassin of U.S. President John F. Kennedy is a former defector to the USSR in the novel, The Tears of Autumn?

The Soviet intelligence and internal security agency in 1963, the Komitet Gosudarstvennoi Bezopastnosti is thrown into a panic when it hears that the assassin of U.S. President John F. Kennedy is a former defector to the USSR, who has recently visited the Soviet and Cuban embassies in Mexico City trying to get readmitted.