SPIEGEL: We have now seen attacks on Charlie Hebdo, then again in Paris on Nov. 13 and this week in Brussels. Have we underestimated the Islamic State (IS) in Europe?
Neumann: We long assumed that, in the West, IS would focus on inspiring single, independent attackers, the so-called "lone wolves." As a result, many security services were taken by surprise that IS could organize relatively complex attacks so quickly and aggressively.
SPIEGEL: Were all security services wrong in their estimation of IS?
Neumann: A high-ranking official of an intelligence service told me that no one apart from the British had anticipated anything like what we have seen. The Americans were aware of course as well, but they always warn of so many scenarios that they at times aren't even taken seriously anymore.
SPIEGEL: Is the "lone wolf" theory -- the idea that an individual can be radicalized and act without instruction -- still accepted?
Neumann: No, but it was never really plausible that this was IS' sole strategy. In January 2015, IS put together teams in Syria which were then sent back to Europe and tasked with carrying out acts of violence. These developments simply went unnoticed.
SPIEGEL: Are there individuals in Germany who have returned from Syria with such missions?
Neumann: Of course.
SPIEGEL: What size are IS' reserves? How many suicide bombers are waiting for their call to action?
Neumann: There are around 5,000 to 6,000 Europeans who have traveled to IS in Syria or in Iraq. Around 15 percent of those are likely to have been killed; between 25 and 50 percent will already have returned. Not every returnee is willing to fight. But, to contrast the situation with al-Qaida, who 10 years ago had perhaps 200 fighters, the number of people they are potentially able to draw upon is a four-digit figure. There aren't just the returnees, but also the supporters in Europe who have never traveled to Syria -- such as the captured Salah Abdeslam.
SPIEGEL: The exchange of information about suspects at the European level is still lacking, despite the establishment of the European Counter Terrorism Center at Europol, the European police agency, and cooperation between intelligence services.
Neumann: Yes, we have no central database in which all the names of individuals likely to threaten public safety or formal suspects are listed. The Left Party in Germany's parliament, the Bundestag, made a small information request last year, and it emerged that the database for foreign fighters contained around 2,000 names -- not even half the number of European jihadists who are fighting abroad. And only five countries provided data at all. Even the Interpol database of stolen and lost passports is rarely used by European countries. We're not talking about a technical problem here, but a political one. If we want the Schengen area to have open borders, then we need to cooperate within it. Even Germany is doing too little in this regard.
SPIEGEL: On top of this is the fact that police forces and security services have different ways of collecting and interpreting data.
Neumann: In part they're even forbidden from sharing data. In Germany, there is a data separation rule (a post-World War II law that stipulates the separation of the work done by police and intelligence services), which is historically justified. We have to accept though that the vast majority of information about jihadist terrorists is in the hands of the secret services. I think it's sensible that the police have greater access to this information. At the moment we have a situation in Europe where the intelligence services' anti-terror task forces are not working with Europol's anti-terror department. In light of the threat posed, this is absurd.
Peter Neumann, 41, is a professor for security studies at King's College in London. In his latest book published in Germany, "The New Jihadists," he warns that Europe is facing a wave of terrorism that will haunt us for decades to come.