German police searched nine apartments and other properties in Berlin and the state of Saxony-Anhalt on Thursday morning as part of ongoing investigations into Germany's Islamist scene in the aftermath of last December's Christmas market truck attack.

According to a joint statement by Berlin police and state prosecutors, a total of 130 officers were involved in the operation, whose main purpose was to collect evidence, "especially data storage devices," at the properties. But no arrests were made.

The searches were part of an ongoing investigation into four suspects, aged between 18 and 21, alleged to either be members of the terrorist organization "Islamic State" (IS) or planning a serious terrorist attack.

The statement said that two of these suspects are thought to have traveled to the Syrian conflict zone via Istanbul, Turkey, in November 2016. A third is thought to have taken part in IS explosives training. All three are believed to be still in Syria and Iraq. The fourth man is under investigation for helping the others by driving them to the airport in Berlin.

The Christmas market in central Berlin attacked last December

Berlin Islamists

The German press has reported additional information, citing unnamed sources in Berlin's security forces, which a spokesman for prosecutors would not confirm. According to the local B.Z. newspaper, the suspects in question had contact with Anis Amri, the Tunisian who drove a truck into a Berlin Christmas market last December, killing 12 people and injuring nearly 100 more. The rejected asylum seeker and former drug dealer was shot dead in Italy a few days after the attack.

One of the apartments raided was reportedly that of Abed El-R., situated close to the Christmas market in central Berlin, who is said to have had close contact with Amri at one point, having met up with him just a week before the attack.

But police do not believe that any of the suspects were direct accomplices of Amri, or that they were planning a terrorist attack in Berlin.

Die Welt newspaper reported that one suspect was overpowered by special police units on Thursday, while two others had been filmed with CCTV cameras watching last year's attack from a nearby shopping mall. But these have since been rejected by police, who said there were no arrests.

A string of raids

German security forces have carried out a number of raids in Berlin in the past few months. At the end of October, police searched a number of properties in the Reinickendorf and Charlottenburg areas of the city, where they discovered a weapons cache of several handguns, rifles, and more than 20 boxes of ammunition containing a total of around 20,000 rounds.

Anis Amri was described as a 'loser' by reporters investigating his case

Authorities at the time said there was cause for concern that these weapons "could be used for attacks," though up to now "there was no evidence of a concrete plan."

Two reporters who produced a documentary for Berlin public broadcaster RBB this week revealed that their investigations showed that Amri had come under the influence of an Islamist preacher named Abu Walaa in the state of North Rhine-Westphalia who encouraged him to carry out an attack.

The reporters described Amri as a "loser" who had failed to make any connections during his 18-month stay in Germany, which began in the summer of 2015, and involved him applying for asylum under various names and nationalities in different states. "What's clear is that he was a petty and a serious criminal, driven by all kinds of different influences," reporter Jo Goll told RBB. "Sometimes he took drugs, sometimes he didn't. Sometimes he consumed pornography, sometimes he didn't. Sometimes he was very religious, sometimes hardly at all. He was a very difficult character, who was looking for a path and who found it in radical Islamism."

Editor's note: Deutsche Welle follows the German press code, which stresses the importance of protecting the privacy of suspected criminals or victims and obliges us to refrain from revealing full names in such cases.