Some 56% of the town's 4,502 inhabitants were Jews prior to World War II. During the invasion of Poland, which started World War II, it was captured and briefly occupied by German forces. On September 12-13, 1939, the "Einsatzgruppe V" entered the town to commit various crimes against the population. Germans sent 350 men, mostly Jewish, to forced labor, of whom only 30 returned after five months. The town was then turned over to the Soviets, who arrested the wealthy residents of the town, including many Jews. Some twenty Jewish families were expelled to Siberia on 21 June 1941 and approximately 2,000 Jews remained in the town. In 1941 the local Polish underground resistance movement was weakened when the Soviets arrested its commander. In June 1941, some 300 Jews were killed in a massacare carried out by the Polish inhabitants of Szczuczyn after the town was bypassed by the invading German soldiers in the beginning of Operation Barbarossa. The June massacre was stopped by German soldiers. A subsequent massacre by Poles in July killed some 100 Jews, and following the German Gestapo takeover in August 1941 some 600 Jews were killed by the Germans, the remaining Jews placed in a ghetto, and subsequently sent to Treblinka extermination camp.