DW: The Office for the Protection of the Constitution notes with increasing alarm that Islamists from Germany go to combat zones. How many are there at the moment?

Hans-Georg Maaßen: We assume that scores of Islamists from Germany are in so-called combat zones. That would be the Afghan-Pakistani border area, Somalia, parts of Libya and, as of late, Syria. Most jihadists are young, aged between 17 and 30, male and with an immigrant background. Over the past years, the number of converts has increased.

How do you rate the situation in Syria?

As far as we can tell, about 40 Islamists from Germany are there at the moment. [Going to] Syria is a trend, not just for people from Germany, but from throughout Western Europe. An estimated 250 to 500 jihadists from Western Europe are in Syria.

Do returnees pose a danger?

We are highly concerned about returnees for several reasons. A main reason being that these are people who presumably have experience fighting, they have handled weapons, know how to make explosives. In addition, they could belong to a terrorist network and be returning with a mission. We are also concerned about people who come back suffused with ideology and who function as a model for a certain clientele.

How well-informed is your agency about radical Islamists in Germany?

I think we have a pretty good overview, in particular where Islamist structures are concerned. Our greatest worry are lone operators that we are not as aware of because they are not obvious on the Internet or in their private lives. Just think of Arid Uka who killed two American soldiers at Frankfurt airport two years ago. No one was aware of the fact that he had become such a radical.

What can you do to prevent attacks from such lone operators?

For one, it is a problem that affects all of society. Each individual can contribute to security. That means if people observe obvious changes in their vicinity, be it at work or within the family, they should notify someone. It is also important that we, the security authorities, continue to be knowledgeable about the Internet; we should know what is going on on social networks so we can recognize whether people are radicalizing themselves.

Should we call the police when our neighbor grows a beard?

I am not speaking up for snitches, but propagating alertness that in my opinion must be part of the self-assured middle classes. People who notice something should pass it on. They do not have to speak to the Office for the Protection of the Constitution or the police, maybe to youth or social authorities.

You said you are well-informed about Islamist structures. How large would you say the 'blind spots' are?

The larger the spot, the sooner you can see it. I don't think we have many large spots, and if there were, chances are good security authorities would spot them. I am more concerned about the many small 'blind spots.' That includes the lone operators who do not communicate within the usual structures and suddenly show up out of the blue.

Before the 9/11, 2001 attacks, the attackers managed to found a cell in Hamburg - unnoticed. Would that still be possible today?

We should be able to recognize structures, organizations and cells. I think in the framework of telecommunication surveillance and with our informants, our authorities are definately capable of recognizing such cell structures. If nothing else, good cooperation with police authorities in the Joint Terrorism Defence Center (GTAZ) - that did not exist before 9/11 - should keep us from experiencing something like that again.

Do ethnic and language barriers make it difficult to observe these structures?

Ethnic and language barriers are always a challenge for us. We meet that challenge with some staff with an immigrant background, so we train our staff accordingly. But it remains to be a challenge because the jihadists are not limited to one ethnic group. There are many different groups, ranging from Somalians, Afghans and Turks to ethnic Germans and other Europeans.

Staff members with an immigrant background faced racist name-calling in your office …

I would like to clarify that there is no racism in my office. I am informed about the incident that occurred in 2009 and that resulted in disciplinary action. It was a quarrel between staff members that involved very, very ugly language - just like it happens in other places. That has nothing to with racism in the office.

Hans-Georg Maassen has been President of Germany's internal security services - the Office for the Protection of the Constitution (BfV) - since August 2012. Before that, the lawyer worked in the Interior Ministry for more than two decades and headed the panel for the fight against terrorism beginning in 2008.

It is the Office for the Protection of the Constitution's function to gather information about groups deemed extremist and espionage activities. The office faces harsh criticism: it is regarded as partially responsible for the fact that the NSU neo-Nazi terror group remained undetected for years while it carried out 10execution-style murders.