German Foreign Fighters in Syria and Iraq: The Updated Data and its Implications
March 10, 2017
Abstract: German security authorities have collected and analyzed data on the majority of the 910 individuals who traveled to Syria or Iraq based on Islamist motivations, the largest such study conducted by any Western government. The analysis confirms earlier findings that there is no typical socio-demographic profile of jihadi terrorists and foreign fighters. With a growing threat emanating from returning foreign fighters, the counterterrorism response needs to be both multifaceted and specific, tailoring approaches to certain sub-groups such as minors, women, converts, and immigrants.
The fact that “Germany is increasingly in the crosshairs of the Islamic State”1 was underscored by the December 19, 2016, terror attack against a Christmas market in Berlin. Although the truck attacker, Anis Amri, did not spend time with a terrorist group overseas, preliminary investigation results indicate he had contact with a radical network in Germany that recruited a significant number of German nationals and residents for the Islamic State in Syria and Iraq.2
The official current estimate is that more than 910 Islamists have left Germany for Syria or Iraq since 2012, although it has not been possible in all cases to verify that these individuals did indeed reach their destination. About one-third of those who departed to join the Islamic State or other Islamist factions are known to be or assumed to be back in Germany. More than 70 of these returnees have experienced armed combat with the Islamic State or at least have undergone some type of military training. About 145 Islamists from Germany are presumed to have been killed in the conflict so far.a
German security authorities (i.e. the police and domestic intelligence agencies at both the Länder (states) and the federal level (including the agency headed by the author—the Criminal Police Bureau, Bremen Police) jointly collected and aggregated information about 784 individuals who had departed Germany to travel to Syria or Iraq before June 30, 2016. This analysis3 was conducted by a task force set up by the Bundeskriminalamt (Federal Criminal Police Agency), the Bundesamt für Verfassungsschutz (Federal Domestic Intelligence Service), and the Hessisches Informations- und Kompetenzzentrum gegen Extremismus (Hessian Center for Information and Expertise on Extremism).
This article outlines and discusses the findings of the official study and examines what the data means for the threat moving forward in Germany. It updates an article co-authored two years ago in this publication by the author, which was based on early official data about German foreign fightersb in Syria and Iraq.4
The Foreign Fighter Flow
Significant numbers of individuals began traveling to Syria or Iraq because of an Islamist motivation in around 2012/2013, reaching a first peak by the third quarter of 2013 according to the official data. After a decline in the rate of departures over the next months, the numbers peaked again in the second quarter of 2014, coinciding with the proclamation of the caliphate by the Islamic State on June 29, 2014, and remained relatively high during the rest of the year. The rate of departures dropped significantly in 2015, however, and has been further declining since that time. For the past year, the number of monthly departures averaged around five, compared to 100 at the peak.
It remains difficult to identify a clear-cut “target group” for jihadi radicalization. Various studies analyzing so-called jihadis in the Western world (i.e. violent extremists claiming an affiliation with Islam) with a focus on shared analysis of investigations of executed or prevented terrorist attacks have been published in the past years, but time and again, such studies confirm the existing intelligence does not support a reliable socio-demographic profile of jihadis.5
The departees included in the official data are 79% male and 21% female. The share of female departees rose significantly after the proclamation of the caliphate in June 2014, climbing from just 15% before the proclamation to 38% in the first year of the post-proclamation phase; since then, it has fallen to 27%. This still very large contingent of female extremists constitutes an exceptional phenomenon not previously encountered, at least on this scale, with regard to jihadism in the West.6
The age range of the departees is 13 to 62 years, with an arithmetic mean age of 25.8 years. The age bracket 22-25 years provides for the largest group (322 individuals), with another 164 departees between 18 and 21 years, and 143 in the 26-29 years bracket. Again, there are considerable differences between the groups who had departed prior to and after the proclamation of the caliphate (henceforth coined “early departees” and “late departees,” respectively). The mean age of the late departees is three years younger than the early departees (23.5 years in the second-post caliphate year, 24.2 years in the first post-caliphate year versus 26.6 years with the early departees); and the percentage of minors (individuals under the age of 18 years) is significantly higher (early departees 5%, first post-caliphate year 11%, second post-caliphate year 16%).7
It should be noted that these numbers include gender specific differences: female departees tend to be significantly younger than their male counterparts (median age 23.5 versus 26.5 years); accordingly, the share of minors among the female departees is considerably higher (13% versus 6% among the males, i.e. nearly four out of 10 departed minors are female). Not included in the report on German foreign fighters compiled by the German agencies are the (substantial) number of children of mostly very young age who were taken by their departing parents. The fates of these children, and the potential threat emanating from them, after growing up in a violence-filled and highly ideologically charged environment such as the Islamic State, however, produces an urgent need to prepare for their reintegration into society.8
Of the 688 individuals with known marital status, 44% were single, 28% legally married, and 22% were married under Islamic law. Two hundred and ninety departees are known to have children. In the last year, however, the share of single individuals without children and/or their own household rose significantly. The reasons why the Islamic State seems to be decreasingly attractive to socially established individuals is not entirely clear from the collected data. One possibility is that the real-life utopia the caliphate presented after its proclamation appealed to radicalized families as well, whereas the current state of decline lost this pull-factor.
Close to 90% of all departees lived in urban areas, with just 13 cities being the place of residence of nearly half of all departees.
Sixty-one percent of the departees were born in Germany, with a broad range of other places of birth (38 countries). The most significant other countries are Turkey (6%), Syria (5%), the Russian Federation (5%), Morocco (3%), and Lebanon (3%). Of the individuals born abroad, 39% immigrated at an age of under 14 years, 23% as teenagers and adolescents,c and 38% at an age of more than 21 years.
Thirty-five percent of all departees have German citizenship exclusively (with significant differences with regard to gender—42% of the women versus 33% of the men). Another 43% hold a dual citizenship including Germany, while 22% hold foreign citizenship.d
Including the individuals born in Germany, a total of 81% of all departees had what German authorities define as a “migration background.”e
The data available on the schooling, training, and occupation of the departees is broad. Seventy-two departees are known to have attended a school at the actual point of their departure. One-hundred and sixteen individuals are known to have begun vocational training. Of these, 42% had completed this training prior to their departure, 32% had dropped out of it before they left Germany, and 26% were still in training when they left Germany. Ninety-four individuals are known to have begun university studies, of whom 10% had completed a degree, 28% had discontinued it, and 63% were still enrolled at the time of their departure. Another 111 individuals are known to have had a regular job at that point, while 166 others were unemployed.
At least 624 individuals are assessed to belong to the core salafi ideological spectrum, while only 29 definitely were not adherents to this religious movement, thus rendering this specific religious outlook by far most important single variable in describing this very heterogeneous group. German domestic intelligence places the current total estimate of salafis in Germany at 9,700, with a persistent upward trend.f This very dynamic movement provides a relatively large recruitment pool from which to draft more jihadis.
At least 134 departees (17% of the total number) are converts. Converts comprised no less than one-third of the female departees, in several cases presumably because of marriage to a Muslim man.g
Two-thirds of the departees have been the subject of criminal investigations (i.e. suspected of or tried for criminal offenses) with significant differences in their delinquent behavior before and after their Islamist radicalization. Prior to Islamist radicalization, property crime and violent attacks (assault, robbery, etc.) were the most common types of criminal activity, with 62% of those with crime links involved in property crimes and 60% of those with crime links involved in violent attacks. The next most common type of crime was drug trafficking (35%). Politically motivated offenses (i.e., criminal acts directed against political or ideological opponents or constituting unlawful support of a political or ideological organization) made up only a small percentage of crimes, 4%.
After the beginning of the radicalization process, the prevalence of crimes that individuals engaged in shifted dramatically, with politically motivated offenses (under German law) perpetrated by more than half of this sub-group (55%), followed by violent attacks (47%) and property crime (41%). Drug-related offenses dropped to just 14%. More than half (53%) of the individuals with a criminal record were suspected of or were tried for three or more offences, including nearly one-third (32%) who had been charged with six or more crimes. More than half of the departees were suspects in ongoing criminal investigations.
These findings correlate with recent studies highlighting the so-called “crime-terror nexus”9—in other words, the apparently growing number of jihadis who originate from petty criminal backgrounds. As Belgian counterterrorism official Alain Grignard has noted, many foreign fighters in this generation appear to be Islamized radicals rather than radicalized Islamists.10
The vast majority of the departees were radicalized in a “real life environment.” The most relevant factors (with multiple aspects possible) for the beginning of the radicalization were like-minded friends (54%), contact with extremist mosques (48%), internet contacts (44%), so-called Islam seminars (27%), organized Qur’an distributions (24%), and family (21%), with contact with extremists in school or prisons accounting for only a very few cases. During the course of the radicalization process, the importance of close social contacts rose even higher, with the most serious impact coming from like-minded friends (63%) and contacts to extremist mosques (57%).
In the majority of cases, the internet (for purposes of distributing propaganda online) played only a supportive and reinforcing role.
In many cases, the radicalization process was very quick. In cases where details on the duration of radicalization are known to the security authorities (only about half of the total), nearly half (46%) of the departees left within one year after the beginning of the radicalization process, with close to a quarter (22%) departing within six months of the start of this process. Overall, 68% of the departees left within two years. Again, there are noteworthy gender differences. The share of female departees among individuals who left within one year of the beginning of the radicalization process is significantly higher (27% versus 18% for male departees).
The analysis concludes that the radicalization process of very quickly radicalized individuals—especially women—“still takes place largely, though not always, out of sight, and that it is more often a self-referential process,”11 (in other words, a radicalization process not predominantly fueled by social contacts, but by inward musings).
Radicalization took place even more quickly after the proclamation of the caliphate. The median duration of the radicalization of the departees dropped from 27 to 20 months. Correspondingly, the share of departees who left Germany within one year after the beginning of their radicalization climbed from 42% to 60% in the post-caliphate declaration phase. In this context, the seemingly real-life implementation of the Islamist utopia seems to have worked as an accelerator for the radicalization process, as it appeared to fulfill the Islamist ideals, thus strengthening and reinforcing the desire to actively take part in this endeavor.
Although individual radicalization normally gets noticed by family, friends, or acquaintances at some point, a surprisingly high number of persons departed before their Islamist radicalization was recognized by others, according to the German official data. Naturally, however, the recognition of an ongoing radicalization would depend on the duration of the individual radicalization process.h/sup>
The Threat from Returning Fighters
The threat posed by the departed Islamists from Germany should be evaluated within the overall jihadi context. The military setbacks the Islamic State have experienced over the last year and a half—including the loss of relatively secure access routes—coupled with the unprecedented surge in refugees from Syria and other Middle East and North African countries to Europe have contributed to a significant change of the threat landscape. The Islamic State quickly adapted and called upon its adherents in Western countries not to try to travel to the so-called caliphate, but to commit terrorist attacks—be they suicide attacks or hit-and-run attacks—in their countries of residence.12 Germany has seen Islamic State sympathizers respond to this call by carrying out attacks involving easily available weapons such as knives; axes; home-made, crude improvised explosive devices; and in the case of the Berlin attack, a truck.13
As the official report correctly points out, the initial success of the Islamic State, and especially the proclamation of the caliphate, mobilized and radicalized significant parts of the German salafi community in an unprecedented way. The ongoing conflict in Syria—and to a lesser extent Iraq—has been used by salafi jihadis to propagate their extremist ideology, focusing on the simple dichotomic message of a constant worldwide, defensive fight between the ummah (the community of the Islamic peoples) and the infidels.14
While the caliphate may have lost its “pull potential” since early 2015, there is no evidence, despite the much slower rate of departures, that the jihadi ideology symbolized by the Islamic State has weakened in strength in Germany and much of Western Europe. German domestic intelligence reports still rising numbers of violence-promoting Islamists in Germany. While 1,000 of the German salafis were considered violent just half a year ago,15 the Federal Office for the Protection of the Constitution (BfV) chief Hans-Georg Maaßen put that number at 1,600 at a conference in late February 2016. The federal criminal police office BKA rates approximately 570 individuals—not all of them currently residing in Germany, however—as “Gefährder,” meaning capable of plotting a terrorist attack.16
In this context, the returning Islamists pose a serious threat to the national security of Germany and Western Europe in general. As of late 2016, approximately 15,000 foreign terrorist fighters are thought to be in Syria and Iraq,17 among them a large number of the 5,000-6,000 who traveled from Europe,18 and many of them will try to return to their countries of origin, especially if they came from Western Europe. Already 30% of the individuals who departed from the European Union are known or assessed to have returned,19 mirroring the rate of returnees to Germany described in the introduction of this article. Given limited resources, the sheer numbers carry the threat of overwhelming the agencies tasked with counterterrorism on domestic soil.20
Radicalized to a jihadi worldview, and in many cases having experienced armed combat with the Islamic State or at least undergone some sort of (para-) military training, the returning foreign fighters are adding lethal capabilities to an already highly adrenalized Islamist community.21 An especially dangerous threat would include the linking up of returning fighters with individuals in their communities who were barred from departure to Syria through administrative measures.
Returning foreign fighters still committed to the cause may choose to continue their jihadi activities on their own or to act under the direction of the dedicated Islamic State operations branch. Training and battlefield experience are elements that most extremists in Germany lacked previously. This reality establishes a challenge to be faced not only within the next couple of years, but most probably for an entire generation.22
Another concern is that given high rates of past criminality among German foreign fighters, many of the returnees will be part of friendship groups with strong ties to criminal activities. They may reestablish these links to support terrorist attacks on German soil—either through crimes as a means of financing or through the procurement of weapons.
Furthermore, in many cases, returning fighters will have developed personal bonds with others abroad, often within certain ethnic groups (for example, European foreign fighters of Chechen descent) that transcend national borders. Just as in the Afghan jihad, the Syrian jihad has created a generation of foreign fighters with international Rolodexes. One example were the foreign fighters from Germany and Austria who joined the Chechen Junud al Sham fighting brigade in Syria. As Guido Steinberg has noted, “The shared experiences of that group created tight bonds between Germans, Turks, Caucasians, and jihadis of other nationalities which will likely shape the nature of the terrorist threat in Germany.”23 These bonds may create networks that are exceptionally hard for security authorities to infiltrate.i
Using the Data to Combat Terrorism
The official data compiled on German foreign fighters and their radicalization trajectories is useful in countering future departures of foreign terrorist fighters and developing a strategy on how to deal with the returnees. As the largest such study conducted by any Western government, it is also useful to policymakers in other countries facing the same threat.
The key findings of the German security services’ study were as follows:
1. Race, country of origin, gender, age, relationship status, educational background, or prior criminal involvement of the departees are so diverse that no universally accepted common denominator could be deduced.
2. Radicalization predominantly takes place in a “real life” environment.j
3. As foreign departures slow from Germany, the pull effect of the so-called caliphate is further diminishing to a nearly non-existent level.
4. The number of individuals trying to return to Germany is increasing.
5. Nearly all departees belong to the salafi religious/ideological stream.
6. Around 80% of the departees have a so-called “migration background.”
7. Certain gender-specific radicalization aspects call for gender-specific prevention activities; women tend to undergo a quicker radicalization process and within the private sphere.
The data shows that there are no simple patterns of radicalization or recruitment of jihadi fighters. Hence, countermeasures need to be both multifaceted and specific. While a full discussion of the types of approaches that may be warranted are beyond the scope of this article, a number of observations can be made.k
The first is that the scale of the foreign fighter problem means that criminal investigations alone will not suffice in tackling it. Due to the challenges the prosecution faces in these cases (including the availability and collection of evidence and the conversion of intelligence into admissible forensic evidence24), the verdicts so far tend to impose sentences of three to four years for the active support of the Islamic State rather than on more concrete charges of murder.25 This means that the threat emanating from these individuals in many cases will be only delayed for a relatively short period of time. It also means there is a strong argument for collaboration between foreign intelligence services (both national and allied ones) and law enforcement agencies to be intensified to try to provide evidence for more serious offenses committed when these individuals were serving the Islamic State.
A second observation is the criminal background of many departees provides law enforcement with opportunities to aggressively pursue criminal investigations into activities of foreign fighters not directly related to terrorist activities, thus providing a different angle for law enforcement operations.
Thirdly, the significant role played by contact with extremist mosques and study circles in the radicalization of German foreign fighters should inform the debate over whether more concerted efforts to proscribe organizations considered a threat to public security, including closing down affiliated gathering places (like clubs or even mosques whose activity breaks German law), are warranted.l While not eliminating the extremist views of the main actors, such measures can counter the establishment and operation of radicalization hubs.
Fourthly, given the increasingly fast pace of radicalization, attempts to counter radicalization efforts directed against possible new recruits in the early stages of radicalization may also be warranted, as well as initiatives developed to deradicalize or disengage known extremists, including returned foreign fighters.26 Although several states and cities have already developed prevention programs and agreed to a coordinated set of preventative and intervention measures directed against Islamist violent extremism, Germany still lacks a national strategym against violent extremism, let alone a coherent national counterterrorism strategy. The findings outlined in this article indicate this strategy would be well advised to deal not only with criminal offenses but with a sort of social—though unlawful—movement. They also indicate a tailored and specialized CVE approach would be helpful, orientated to specific sub-groups, whether women, people with migration background, or other identifiable clusters.
The foreign fighter phenomenon already has a societal impact reaching far beyond the scope of law enforcement and public security. This ‘fallout’ may include polarization between political, ethnic, or religious groups or a rising anxiety within the population leading to a “securization of society,”27 requiring countermeasures on a political level within a comprehensive strategic approach. In the meantime, the terrorist threat in Germany, as in many other Western European countries, remains at an all-time high. Law enforcement agencies as well as domestic intelligence agencies at both the federal and state level will have to remain vigilant, and returning foreign fighters will be among the top of their list of persons of interest. CTC
Dr. Daniel H. Heinke is the director of the Landeskriminalamt (LKA), the state bureau of investigation, in Bremen, Germany, and the Chief of Detectives, Criminal Police Bureau, Bremen Police. He is also an adjunct professor of terrorism studies at the HfÖV Bremen and an associate fellow at the International Centre for the Study of Radicalisation and Political Violence (ICSR), King’s College London. Follow @daniel_heinke
[a] This is as of March 1, 2017. (Source: Ministry of the Interior, Free Hanseatic City of Bremen, Germany).
[b] For purposes of this article, German foreign fighters include all Islamists who traveled or attempted to travel to jihadi battlegrounds overseas from Germany, including German nationals and residents.
[c] German law differentiates between “youths” (age 14-17) and “adolescents” (age 18-20).
[d] The largest groups of foreigners have citizenships of Turkey (14% of the total number) and Russia (4%), with Syria, Morocco, and Tunisia the next most represented.
[e] In Germany, individuals with a migration background are officially defined as “all persons who have immigrated since 1949 to the territory that today constitutes the Federal Republic of Germany, all foreigners born in Germany, and all German nationals born in Germany who have at least one parent who immigrated to Germany or who was born as a foreigner in Germany.” See Bundesamt für Statistik (Federal Statistical Office) for further details.
[f] This is as of March 1, 2017, per the Ministry of the Interior, Free Hanseatic City of Bremen, Germany.
[g] Two years ago, Jessica Stern and J.M. Berger highlighted the disproportionately high number of converts among Western foreign fighters, confirming a historically well-known phenomenon. Jessica Stern and J.M. Berger, ISIS: The State of Terror (New York: HarperCollins, 2015), p. 81.
[h] The analysis provides detailed information on the outward signs of the individual radicalization that is not relevant to this article. See Daniel H. Heinke, “Foreign Terrorist Fighters: German Islamists in Syria and Iraq and What Can be Done About Them,” Marshall Center Security Insights No. 15 (2016).
[i] Another threat to public security are returning fighters who turn their back on jihadism but choose to employ skills obtained in jihadi battle-zones within organized crime groups. Martin Gallagher, “‘Criminalised’ Islamic State Veterans – A Future Major Threat in Organised Crime Development?” Perspectives on Terrorism 10:5 (2016): pp. 51-67.
[j] Editor’s note: Georg Heil illustrated the various aspects of such a “real life environment” with the example of the German Abu Walaa network. See Georg Heil, “The Berlin Attack and the Abu Walaa Islamic State Recruitment Network,” CTC Sentinel 10:2 (2017). Jan Raudszus presented another interesting case study in “Der Tag des Verführers,“ Die Zeit, September 29, 2016.
[k] It should also be pointed out that administrative measures aimed at preventing individuals from departing to Syria, such as the requirement to report to police stations at certain intervals and the withdrawal of passports and other identity documents, will not be very effective in combating the threat from foreign fighters who have already returned to Germany.
[l] Editor’s note: Georg Heil described how a mosque in Heidelberg and a “madrassa” in Dortmund were allegedly used to indoctrinate individuals by the extremist network Abu Walaa. See Georg Heil, “The Berlin Attack and the Abu Walaa Islamic State Recruitment Network,” CTC Sentinel 10:2 (2017).
[m] The Bremen state Minister of the Interior proposed such a strategy, arguing it was imperative to provide for the necessary vertical (federal government, states, municipalities) as well as horizontal (departments of the interior, justice, education, social affairs, etc.) coordination of all relevant actors. See Daniel Heinke, “Warum Deutschland eine Nationale Präventionsstrategie gegen gewaltbereiten Extremismus braucht,” Sicherheitspolitik-Blog, June 1, 2015.
 Florian Flade, “The Islamic State Threat to Germany: Evidence from the Investigations,” CTC Sentinel 9:7 (2016).
 Georg Heil, “The Berlin Attack and the Abu Walaa Islamic State Recruitment Network,” CTC Sentinel 10:2 (2017).
 “Analysis of the background and process of radicalization among persons who left Germany to travel to Syria or Iraq based on Islamist motivations,” German Security Services, December 7, 2016. See https://www.bka.de/SharedDocs/Downloads/EN/Publications/Other/AnalysisOfTheBackgroundAndProcessOfRadicalization.html?nn=53602.
 See Daniel Heinke and Jan Raudszus, “German Foreign Fighters in Syria and Iraq,” CTC Sentinel 8:1 (2015). This study examined official German data collected in December 2014 on 378 German foreign fighters.
 Daniel H. Heinke, “Countering Radicalization and Recruitment of so-called Jihadists: Proscription of Radicalization Hubs,” Defense Against Terrorism Review 8 (2016): pp. 89-97. For an overview of the situation in Europe, see Bibi van Ginkel and Eva Entenmann eds., The Foreign Fighters Phenomenon in the European Union (The Hague: International Centre for Counter-terrorism, 2016). For a more detailed overview on previous research and the radicalization process, see Daniel H. Heinke and Ryan Hunter, “Radicalization of Islamist Terrorists in the Western World,” FBI Law Enforcement Bulletin 80:9 (2011): pp. 25-31.
 Daniel H. Heinke, “Foreign Terrorist Fighters: German Islamists in Syria and Iraq and What Can be Done About Them,” Marshall Center Security Insights No. 15 (2016): p. 2. For further discussion of this topic, see Elizabeth Pearson, “What is Luring Western Women to Syria to join ISIL?” Telegraph, February 25, 2015, and Louisa Tarras-Wahlberg, Promises of Paradise? A Study on Official ISIS Propaganda Targeting Women (Stockholm: Swedish Defence University, 2016).
 For a more detailed discussion of the links between adolescence and radicalization, see Daniel H. Heinke and Mareike Persson, “Youth Specific Factors in Radicalization,” Defense Against Terrorism Review 8 (2016): pp. 53-66.
 Heinke, “Foreign Terrorist Fighters: German Islamists in Syria and Iraq and What Can be Done About Them;” “Initiative to Address the Life Cycle of Radicalization to Violence: Neuchâtel Memorandum on Good Practices for Juvenile Justice in a Counterterrorism Context,” Global Counterterrorism Forum, 2016. See also Mia Bloom, John Horgan, and Charlie Winter, “Depictions of Children and Youth in the Islamic State’s Martyrdom Propaganda, 2015-2016,” CTC Sentinel 9:2 (2016): pp. 29-32.
 Rajan Basra, Peter R. Neumann, and Claudia Brunner, Criminal Pasts, Terrorist Futures: European Jihadists and the New Crime-Terror Nexus (London: The International Centre for the Study of Radicalisation and Political Violence, 2016); Rajan Basra and Peter R. Neumann, “Criminal Pasts, Terrorist Futures: European Jihadists and the New Crime-Terror Nexus,” Perspectives on Terrorism 10:5 (2016): pp. 25-40; Martin Gallagher, “‘Criminalised’ Islamic State Veterans – A Future Major Threat in Organised Crime Development?” Perspectives on Terrorism 10:5 (2016): pp. 51-67.
 Paul Cruickshank, “A View from the CT Foxhole: An Interview with Alain Grignard, Brussels Federal Police,” CTC Sentinel 8:8 (2015): pp. 7-10.
 “Analysis of the background and process of radicalization among persons who left Germany to travel to Syria or Iraq based on Islamist motivations,” p. 49.
 Abu Muhammad al-Adnani, “That They Live by Proof,” Al-Furqan, May 21, 2016.
 For details on the attacks, see Flade.
 For a detailed discussion of the extremist ideology, see Heinke and Hunter.
 Paul Cruickshank, “A View from the CT Foxhole: Hazim Fouad and Behnam Said, Analysts at the Bremen and Hamburg Verfassungsschutz,” CTC Sentinel 9:7 (2016): pp. 7-10.
 “German intel agency notes dramatic increase in Islamic extremism,” Deutsche Welle, February 22, 2017.
 Tanya Mehra, Foreign Terrorist Fighters: Trends, Dynamics and Politics Responses (The Hague: International Centre for Counter-terrorism, 2016), p. 7.
 Petter Nesser, Anne Stenersen, and Emilie Oftedal, “Jihadi Terrorism in Europe: The IS-Effect,” Perspectives on Terrorism 10:6 (2016): pp. 3-24.
 Mehra, p. 7.
 Christopher J. Wright, “How Dangerous Are Domestic Terror Plotters with Foreign Fighter Experience? The case of Homegrown Jihadis in the US,” Perspectives on Terrorism 10:1 (2016), pp. 32-40.
 James Howcroft, “Dare to share: How to put intelligence to work against ISIS terrorists returning from Syria to their countries of origin,” The American Interest, December 1, 2016. For more on the threat of returning foreign fighters, see Thomas Hegghammer, “Should I Stay or Should I Go? Explaining Variation in Western Jihadists’ Choice between Domestic and Foreign Fighting,” American Political Science Review 107:1 (2013), pp. 1-15.
 Peter R. Neumann, Die neuen Dschihadisten: ISIS, Europa und die nächste Welle des Terrorismus (Berlin: Econ, 2015), p. 135.
 Guido Steinberg, “Junud al-Sham and the German Foreign Fighter Threat,” CTC Sentinel 9:2 (2016): pp. 24-27.
 Mehra, p. 8; Behnam T. Said, Islamischer Staat. IS-Miliz, al-Qaida und die deutschen Brigaden (Munich: C.H.Beck, 2nd Ed., 2014), p. 172.
 Peter R. Neumann, Der Terror ist unter uns. Dschihadismus und Radikalisierung in Europa (Berlin: Ullstein, 2016), p. 250.
 See Bart Schuurmann and Liesbeth van der Heide, Foreign fighter returnees & the reintegration challenge – RAN Issue Paper (The Hague: Radicalisation Awareness Network – Centre of Excellence, 2016).
 See Jeanine de Roy van Zuijdewijn, “Terrorism and Beyond: Exploring the Fallout of the European Foreign Fighter Phenomenon in Syria and Iraq,” Perspectives on Terrorism 10:5 (2016): pp. 82-96.