The Ustaše movement's grievances centred around the perceived injustices inflicted upon the Croats in Serb-dominated Yugoslavia during the interwar period. Senior Ustaše officials cited the shooting of five Croatian parliamentary deputies in June 1928, the murder of the Croatian nationalist anthropologist and historian Milan Šufflay in 1931, the suppression of the Velebit Uprising in 1932, the murder of the Croatian Peasant Party vice-president Josip Predavec in 1933, and the arrest and incarceration of dozens of other Croatian political figures. In early April 1941, Luburić had illegally crossed the Yugoslav border near the town of Gola. By mid-April, he arrived in Zagreb and was appointed to the Economic Bureau of the Main Ustaša Headquarters (; GUS), the Ustaše ruling body, serving as an adjutant to Vjekoslav Servatzy. On 6 May, Luburić was dispatched to the village of Veljun, near Slunj, to lead the round-up of 400 Serb males from the village in retaliation for the murder of a Croat family in neighbouring Blagaj the night before. Although the identity of the perpetrators remained a mystery, the Ustaše announced that the Serbs of Veljun were responsible and decided that the village's male inhabitants were to be collectively punished. Luburić had a total of 50 men at his disposal, many of them longtime Ustaše who had lived in exile in Italy in the 1930s. On the evening of 9 May, the Serb males of Veljun were brought to Blagaj, and killed with knives and blunt objects in the backyard of a local elementary school. The murders lasted all night. The following morning, Luburić was seen emerging from the school covered in blood, washing his hands and sleeves by a water well. In late June, Ustaše officials driving through the villages of Gornja Suvaja and Donja Suvaja, in the Lika region, reported being shot at, prompting the regional authorities to order a "cleansing" action against the villages. On the morning of 1 July, Luburić led a group of Ustaše into the two villages. The historian Max Bergholz writes that up to 300 Ustaše took part in the operation. According to the journalist and Holocaust survivor Slavko Goldstein, Luburić had about 150 members of the Ustaše Auxiliary Force at his disposal, in addition to 250 members of the Croatian Home Guard.