BERLIN (AP) — Police in Germany on Friday raided the homes and businesses of four men linked to the Islamic State sympathizer who carried out a deadly shooting in the Austrian capital of Vienna this week.

Austria, meanwhile, announced the temporary removal of several officials over errors made before the attack and ordered the closure of two Vienna mosques that had been visited by the gunman.

German police, including members of the anti-terrorism unit GSG9, searched premises in the central city of Kassel, Osnabrueck in the northwest and in Pinneberg county near Hamburg.

Police said that while the men weren’t currently suspected of involvement in Monday’s shooting, there was evidence that they had links to the attacker.

Four people were killed in the attack, and the gunman also died. Twenty others, including a police officer, were wounded.

German federal prosecutors said that two of the men whose premises were searched were believed to have met the attacker in Vienna this summer. A third man had contact with him online, while the fourth had no direct contact to the attacker but was in touch with people who knew him.

Prosecutors said they were trying to collect possible evidence during the searches and that nobody was arrested.

Authorities in Austria have identified the attacker as 20-year-old Kujtim Fejzulai, a dual national of Austria and North Macedonia who had a previous conviction for trying to join IS in Syria and had been given early release in December.

An investigation has been launched into why Austria didn't put Fejzulai under observation despite being tipped off by Slovakian authorities that he had tried to purchase ammunition at a shop in Bratislava in July.

Austrian authorities detained 16 people in the country in connection with the attack. Four of them had previous terror-related convictions and several others also had criminal records.

Eight of them have now been ordered held in custody pending possible formal charges, while six have been released, news agency APA reported.

Authorities in neighboring Switzerland also took two people into custody this week.

Amid concerns that authorities missed warnings signs leading up to the attack, officials said Friday that the head of the Vienna regional anti-terrorism agency has stepped aside from his post and several other officials involved in the investigation are also being replaced.

“There were, in our view, intolerable errors made in the investigation,” Interior Minister Karl Nehammer told reporters.

Austrian authorities also announced that they have ordered the closure of two mosques in Vienna that were frequented by the attacker. About 70 police were involved in shutting down the two mosques Friday.

Susanne Raab, Austria's minister for integration, said the mosques were deemed to have provided what she described as “a breeding ground for dangerous ideology.”

“I want to emphasize that it's not a fight against Muslims in Austria," she said. "We're all fighting together, because Muslims in Austria are also among those who are particularly threatened by political Islam and radicalism.”