Complex sentence: One of the prisoners who spoke fluent German, highlighted their case to the officer and sympathetic to their plight later organized the movement of the airmen from Buchenwald to Stalag Luft III in Poland.
Split into simpler sentences: One of the prisoners who spoke fluent German, highlighted their case to the officer. Sympathetic to their plight, he later organized their movement from Buchenwald to Stalag Luft III in Poland.