Complex sentence: On 13 or 14 March 1938, on Heydrich's orders, Böhme murdered Wilhelm Freiherr von Ketteler (by drowning him), an attaché at the German embassy in Vienna, who was hated by the SS because of his anti-Nazi activities.
Split into simpler sentences: On 13 or 14 March 1938, on Heydrich's orders, Böhme murdered Wilhelm Freiherr von Ketteler by drowning. Ketteler was an attaché at the German embassy in Vienna, who was hated by the SS because of his anti-Nazi activities.