Complex sentence: Matlock continued to advise the President on policy toward the Soviet Union and on September 1,1983, when the Soviets shot down commercial flight KAL 007, Matlock returned to Washington to work with White House officials.
Split into simpler sentences: Matlock continued to advise the President on policy toward the Soviet Union. When, on September 1,1983, the Soviets shot down commercial flight KAL 007, Matlock returned to Washington to work with White House officials.