DW: You were one of the first people with access to the Snowden documents, some of which were classified as strictly confidential. What shocked you the most when reading them?

Holger Stark: I was particularly fascinated by how early the NSA categorized the Internet as a medium for full-scale monitoring. There was a passage in the documents of former NSA chief Kenneth Minihan from the summer of 1996 where he confidentially tells his colleagues that the Internet is the key medium of the future, comparable to the invention of the atom bomb in the 20th century. Minihan says that whoever controls the Internet has the power in the 21st century. And he adds that all efforts need to serve the goal of asserting America's intelligence dominance.

You have already published six feature pieces on the NSA scandal. Now you have written the book "The NSA Complex" with your colleague Marcel Rosenbach. Are we slowly starting to get the full picture of organized mass surveillance?

The NSA systematically taps fiber optic cables - the main arteries of Internet traffic conveying the largest streams of data. It engages some American companies as collaborators and cooperates with partner intelligence agencies abroad, including Germany's Federal Intelligence Service [also known by its German acronym, BND]. This system enables control of nearly the whole stream of relevant data and then processing it with sophisticated intelligence analysis programs to see what is important.

I think we have grasped this principle, but the material is so extensive that we will still be seeing interesting and partly surprising and shocking reports about it over many months.

As a partner in this systematic surveillance, does Germany have a small advantage?

Germany is a victim on the one hand and a co-perpetrator on the other. In various areas, the German government is one of the NSA's targets. The most spectacular of these was definitely the bugging of the German chancellor's cell phone, but the files also contain records of other Germans being monitored. And the Foreign Intelligence Surveillance Court (FISC) - the special US court for these matters - issued a verdict that monitoring Germany is legitimate.

At the same time, as a member of a joint secret-service operation, Germany is one of the NSA's partners. The Federal Intelligence Service conducts various activities together with the NSA related to the fiber optic cables carrying Internet data. The Federal Intelligence Service organizes access and then shares the data with the NSA.

In the book you demonstrate that spying by surveillance agencies also extends to medium-size businesses in Germany.

Stark (left) wrote the book together with fellow 'Der Spiegel' journalist Marcel Rosenbach (right)

The NSA and Britain's Government Communications Headquarters (GCHQ) consider very carefully which companies could be of interest to them. This includes technology firms that are leaders in their respective fields; that possess unique technological expertise. And they look to see which businesses offer something really special.

For example, there are numerous German companies that offer Internet per satellite in places such as outlying parts of Africa. These companies are interesting because they are entering regions that are of special interest to the NSA. In cases like this, the NSA targets company employees such as technicians and engineers. They hack into computers and routers and attempt to intercept the joining point between the satellites and normal Internet cables.

Does the White House still have control over US intelligence services?

This is one of the noteworthy insights that we gained from reading through the documents: The NSA doesn't generally do anything that hasn't been sanctioned by the White House. Every six months, the White House issues a type of "surveillance matrix" - in which all countries and topics of interest are outlined: foreign policy, armament policy, economic policy and similar things. For each country, a very sophisticated information-sifting process determines what the interests are and how high the priorities are. One is very high and five is very low.

In cases like China, Iran, and North Korea, a one can be found everywhere in this table. For Germany it's a mixture of threes and fours. This overview is very systematically processed by the NSA. It’s not as if the agency is just taking wild stabs in the dark without the captain’s knowledge.

In Germany, the NSA investigation committee has sprung into action. Does it have any chance of looking behind the scenes and seeing how the agency operates?

The job will be difficult for the investigation committee - because it's a committee that can't investigate the NSA, since the NSA won't share any solid information with the German parliament. This means that the committee will have to be satisfied with access to public documents and explore the other side to see what the German intelligence services did together with the NSA. That's why I assume that at least half of the committee's investigations will deal with the Federal Intelligence Service and possibly also with the Federal Office for the Protection of the Constitution [Germany’s domestic intelligence service]. I don't expect the committee to be able to answer all the questions.

Holger Stark is a Washington-based correspondent for the German current affairs magazine "Der Spiegel." Together with Marcel Rosenbach, one of the magazine's editors, he published a book titled "Staatsfeind WikiLeaks" ("State Enemy WikiLeaks"), covering Chelsea Manning's leakage of US classified documents. The authors' new book, "Der NSA-Komplex" ("The NSA Complex"), is now out in German.