Austrian police are investigating whether an Islamist terrorist who killed four people in Vienna on Monday night was part of a wider network and if the attack could have been prevented. Kujtim Fejzulai, known to authorities as a sympathiser of the Islamic State group, which claimed credit for the murders, is believed to have been the lone gunman in the attack despite hours of uncertainty over whether accomplices remained at large. The 20-year-old dual citizen of Austria and North Macedonia was shot dead nine minutes into the attack in central Vienna. Police in Austria carried out raids at 18 properties linked to the attacker on Tuesday and made 14 arrests. Two men were also arrested in the Swiss city of Winterthur, near Zurich, after reports Fejzulai had met them in Switzerland. Fejzulai is also believed to have travelled to neighbouring Slovakia in July accompanied by another man, where he attempted to buy ammunition suited to the weapons he used in the attack, but the sale reportedly fell through after he failed to produce a firearms licence. Slovakian authorities are said to have informed their Austrian counterparts at the time. The men travelled in a car registered in the name of the mother of an Islamist known to police. Austria’s interior minister, Karl Nehammer, said on Tuesday that Fejzulai was known to the authorities as a sympathiser of Isis. He had been sentenced to 22 months in an Austrian prison on 25 April 2019 for affiliation to a terror organisation, after attempting to cross from the Turkish border – where he had met two Germans and a Belgian – into Syria. The sentence was suspended in December last year on condition he would be regularly monitored by probation services and would participate in a deradicalisation programme. Nehammer and the Austrian chancellor, Sebastian Kurz, both of the conservative People’s party, have criticised his premature release from jail. Nehammer said Fejzulai had been able to deceive his mentors in such a way that they registered no early warning signs of his radicalisation. He said it pointed to “a faultline in our system”, which had allowed for “a premature release of a radicalised person”. Alma Zadić, the justice minister, of the Green party, defended the decision, saying it was legal and that he had been released on parole. The justice ministry later said it had not been informed about Fejzulai’s attempts to buy ammunition in Slovakia, saying it would have been reason to arrest him. The government was meeting on Wednesday to discuss the security situation and whether the attack might have been prevented. Reinhold Einwallner, of the Social Democratic party, said he was astounded that the attacker’s attempt to buy ammunition, particularly when his affiliation with Isis was known, had not triggered a security alert. “It should have caused alarm bells to ring,” he told the Austrian newspaper Kurier. He called for a more intense exchange of information between the justice and interior ministries about people considered a security threat, saying: “the number of IS [Isis] returnees is of a manageable size.” The justice ministry said it had not been informed about Fejzulai’s attempts to buy ammunition in Slovakia, saying it would have been reason to arrest him. The populist far-right Freedom party said the role of the intelligence service urgently needed to be examined. “There are numerous indications that this terrorist and the circles he moved in, had been on the intelligence services’ radar for a long time. And if that was the case, why was this terrorist not taken off the streets?” Herbert Kickl of the party said. Nikolaus Rast, a lawyer who acted for Fejzulai, said his client had drifted through life and was “easy prey” for terror groups. “He left the impression on me of being a young man searching for something, who didn’t know what his place in society was, who had failed to find an appropriate apprenticeship position and was therefore easy prey for certain groups,” he told the tabloid Bild. Three men, two of Turkish origin and another who is Palestinian, were being hailed as heroes for having risked their lives at the scene of the attack to help some of the injured. Mikail Özen, 25, and Recep Tayyip Gültekin, 21, were about to park their car on Schwedenplatz ahead of enjoying a last coffee together before a coronavirus lockdown when the shooting started. They ran to the aid of a woman they saw lying on the ground, and Gültekin was shot at. “The attacker fired at him. But Recep was able to intuitively save himself by doing a forward roll,” Özen said. They managed to take the woman to safety. Osma Yoda, 23, who had been working in a McDonald’s on the square, was helping his boss carry boxes when they came across the gunman. “He was hidden in a closed garage entrance and was shooting at passersby,” the Palestinian man said. When two police arrived, the gunman shot at them, striking one of them. “I dragged him behind a concrete bench and tried to stop the bleeding,” Yoda told Kurier. “He continued to fire from a distance of around 20 to 30 metres. There was blood everywhere.” He then helped officers take him to a nearby ambulance, assisted by Gültekin and Özen, who are both amateur martial artists. The men were received by both the Turkish ambassador in Austria and the mayor of Vienna, who thanked them for their actions. A police officer on duty on the night of the attack described the confusion and chaos as he and colleagues attempted to secure the bars and restaurants in the area. “The bullets kept coming and we were rescuing injured people, but we didn’t know where to take them, because we didn’t know where the arsehole was,” he told the Austrian news agency APA. The 27 people injured, who sustained both gunshot and stabbing wounds, were said to no longer be in critical condition. Among the dead was said to be a female student at the University of Applied Arts.