Complex sentence: Andrés Nin was murdered, under direct orders from Stalin and the supervision of the NKVD, by the Republican Government's secret police on June 20; apparently "Comandante Contreras" Vittorio Vidali, and Iosif Romualdovich Grigulevich were involved.
Split into simpler sentences: Andrés Nin was murdered, under direct orders from Stalin and the supervision of the NKVD, by the Republican Government's secret police on June 20. Apparently "Comandante Contreras" Vittorio Vidali, and Iosif Romualdovich Grigulevich were involved.