KRAKOW, Poland -- The 24-year-old gunman who killed six people and wounded 15 others in a Polish city square died in a hospital on Monday, police said. The attacker, wearing military-style clothing and a bulletproof vest, drove into the main square in Krakow’s Old Town on Saturday and opened fire. The square is a major tourist destination in Poland’s second-largest city. Several foreigners were among the dead and wounded. The gunman, Michał Oksiński, died at 4:30 a.m., authorities said. He had been in critical condition since the attack and had undergone several operations. Authorities also found the bodies of his sister, mother and father at the family home in Ostrowiec Świętokrzyski, about 150 kilometres northeast of Krakow. They likely died from gunshot wounds. Authorities investigating the motive Interior Minister Marcin Kierwiński said Saturday that Oksiński held “very radical” and “ultranationalistic” views. Authorities were still examining the evidence Monday. “We are first of all investigating if he was inspired by anyone, if someone helped him,” Eryk Stasielak of the Krakow branch of the national prosecutor’s office told The Associated Press. “We have secured his electronic devices and we will try to open them and get to the contents.” Interior Ministry spokesperson Karolina Gałecka said that authorities were examining the meaning of numerous symbols and patches sewn onto Oksiński’s clothing or found at his home. Prosecutors said they found a yellow flag bearing a black snake, known as the Gadsden flag, hanging on the wall of the attacker’s room. The flag originated during the American Revolution and was later adopted by the U.S. Tea Party movement. Authorities said they believed Oksiński killed his family, possibly while they slept, before heading to Krakow. Seven weapons were found in the family home, bringing the total recovered to 11, prosecutors said. Four, including two AR-15 semi-automatic rifles, were found on Oksiński or in his car in Krakow. Dozens, if not hundreds, of shots were fired during the attack, they said. Oksiński and his father held gun permits. He had trained at a local shooting club, which said in a statement that he “was never trained in our club in the areas of dynamic, tactical or combat shooting.” World facing threats from lone actors Mass shootings are uncommon in Poland. However, in mid-October three attacks at schools in the central province of Mazovia took place within four days, leaving one person dead and many wounded, including children. The attackers used knives or sharp objects and some were said to be interested in the far-right. Polish Prime Minister Donald Tusk said the school attacks were fuelled by the online “glorification of violence.” He said the acts could be associated with “nihilistic violence,” a term used by authorities to describe acts of violence driven by a nihilistic worldview and misanthropy rather than specific political goals. Oksiński’s military-style equipment and weapons were similar to those of other “extreme right lone actors” committing attacks around Europe and the world, said Kacper Rekawek, a senior researcher at the International Centre for Counterterrorism in The Hague. “We have had attempts before, but now we can say that these kinds of attacks have become successful in Poland.” Rekawek said that even without an explicit link between the Krakow attack and incidents of school violence, they could be viewed as part of “a series.” ‘Heroic’ police officers prevented more victims A video posted on social media showed a police officer repeatedly firing at Oksiński as he lay in the street. An image of the wounded officer kneeling beside the attacker has since gone viral in Poland. “Senior police officers Jakub Kulik and Artur Morański are real heroes,” Tusk wrote on X. “They most likely saved the lives of many human beings, without regard for the risk of losing their own lives. Their state is serious, but they are under very good care. All Poland keeps fingers crossed for you.” The two officers were patrolling the area when they were called to intervene. Police fired the first shot within three minutes of receiving the initial report. The officers chased the attacker and fired at him with their service weapons as he fired a semi-automatic rifle. Kulik continued firing even after he was shot. Both officers were seriously wounded. Kulik, 24, was in critical condition, prompting officials to issue an urgent appeal for blood donations. A fundraiser for the officers and their families has so far raised more than 6 million zlotys (US$1.5 million). Krakow’s mayor announced that both officers would be named honorary citizens of the city. Two surgeons who happened to be nearby during the attack helped save the officers’ lives. “He took care of the officer who subdued the attacker because he truly needed urgent help,” Krakow surgeon Michał Pędziwiatr said of fellow surgeon Mateusz Wierdak. “Without protection, without gloves, he simply focused on the officer, stopping the bleeding in his chest. This probably saved his life.” Talented artists among the victims Izabela Woźna, a 53-year-old painter and mother of four, was killed in the attack. She had opened an exhibition of her work in Krakow on Friday evening. Krakow Academy of Fine Arts confirmed that Magdalena Oksińska -- the suspect’s sister -- had been one of its third-year students. It said an employee’s sister had also been shot twice. “Nothing will ever be like before. The delicate tissue of our academic community was painfully wounded,” the academy said in a statement Sunday. “Magdalena Oksińska, 21 years old, a queer person, was an absolutely talented painter, photographer, poet and writer,” architect Pavko Krajka wrote in a social media post accompanied by images of her colorful paintings. “Her death is a great loss for Krakow, Polish, European and queer culture.” By Rafal Niedzielski, Claudia Ciobanu And Beata Zawrzel