On Thursday, German police went door to door in a series of raids targeting suspected Islamic jihadists. The terrorists were allegedly planning several attacks in Germany and other parts of Europe. Many of the suspects were refugees brought to the German soil with the full faith and credit of Chancellor Angela Merkel.

Security sources told DPA [German news wire service] the group’s ringleader was a 35-year-old Algerian arrested in North Rhine-Westphalia. "The man, who was staying in refugee accommodation in the town of Attendorn, was also being sought by Algerian authorities due to a suspected connection to ISIS, with whom he is said to have undergone military training in Syria,” reports Germany’s The Local. “DPA also reports that the man arrived as an asylum seeker in Germany in autumn 2015 after travelling through Europe via the so-called Balkan route, which starts in Greece and passes through Macedonia and Serbia.”

All of the suspected terrorists are linked to the civil war in Syria. Some may have links to ISIS.

After the mass sexual assault in Cologne, German authorities have been reconsidering security procedures, clamping down on suspected terrorists with unprecedented force. “In Berlin, 450 police officers searched four apartments and two businesses, arresting another Algerian man in the process,” adds The Local. Police surveilled the suspects for several weeks before they gathered enough evidence to greenlight a full-scale raid.

Still, Berlin’s interior minister, Frank Henkel, admits that an Islamic terrorist attack in Germany is inevitable. It’s not a matter of if, but when. “We have every reason to stay alert and be careful,” asserts Henkel.

See below for images of the raids: