BERLIN (AP) — German investigators said Friday they have shut down a data processing center installed in a former NATO bunker that hosted sites dealing in drugs and other illegal activities. Seven people were arrested.

The main suspect in the long-running investigation that led to raids on Thursday is a 59-year-old Dutchman who authorities believe acquired the former military bunker in Traben-Trarbach, a picturesque town on the Mosel River in western Germany, in 2013, prosecutor Juergen Bauer told reporters.

He then turned it into a very large and heavily secured data processing center “in order to make it available to clients, according to our investigations, exclusively for illegal purposes,” Bauer added. Regional criminal police chief Johannes Kunz said that authorities believe he had “links to organized crime,” and that he appears to have spent most of his time in the area although he was registered as having moved to Singapore.

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Thirteen people aged 20 to 59 are under investigation in all, including three German and seven Dutch citizens, Brauer said.

Authorities arrested seven of them, citing the danger of flight and collusion. They are suspected of membership in a criminal organization because of a tax offense, as well as being accessories to hundreds of thousands of offenses involving drugs, counterfeit money and forged documents, and accessories to the distribution of child pornography. Authorities didn’t name any of the suspects.

The data center was set up as what investigators described as a “bulletproof hoster,” meant to conceal illicit activities from authorities’ eyes.

Investigators say the platforms it hosted included “Cannabis Road,” a drug-dealing portal; the “Wall Street Market,” which was one of the world’s largest online criminal marketplaces for drugs, hacking tools and financial-theft wares until it was taken down earlier this year; and sites such as “Orange Chemicals” that dealt in synthetic drugs. A botnet attack on German telecommunications company Deutsche Telekom in late 2016 that knocked out about 1 million customers’ routers also appears to have come from the data center in Traben-Trarbach, Brauer said.

The arrests took place at a restaurant in the town and in Schwalbach, outside Frankfurt. Alongside the raids in Germany, there were searches in the Netherlands, Poland and Luxembourg.

“I think it’s a huge success ... that we were able at all to get police forces into the bunker complex, which is still secured at the highest military level,” Kunz said. “We had to overcome not only real, or analog, protections; we also cracked the digital protections of the data center.”