Complex sentence: Straight did not confess when interviewed about Burgess and Maclean in 1951, but when offered a job in the Kennedy Administration, in 1963, Straight revealed his knowledge of Blunt.
Split into simpler sentences: Straight did not confess in 1951, when interviewed about Burgess and Maclean. But when offered a job in the Kennedy Administration, in 1963 Straight revealed his knowledge of Blunt.