In September 1939, after Germany invaded Poland, Begin, in common with a large part of Warsaw's Jewish leadership, escaped to Wilno (today Vilnius), then eastern Poland, to avoid inevitable arrest. The town was soon occupied by the Soviet Union, but from 28 October 1939, it was the capital of the Republic of Lithuania. Wilno was a predominately Polish and Jewish town; an estimated 40 percent of the population was Jewish, with the YIVO institute located there. As a prominent pre-war Zionist and reserve status officer-cadet, on 20 September 1940, Begin was arrested by the NKVD and detained in the Lukiškės Prison. In later years he wrote about his experience of being tortured. He was accused of being an "agent of British imperialism" and sentenced to eight years in the Soviet gulag camps. On 1 June 1941 he was sent to the Pechora labor camps in Komi Republic, the northern part of European Russia, where he stayed until May 1942. Much later in life, Begin recorded and reflected upon his experiences in the interrogations and life in the camp in his memoir "White Nights".