He was appointed a member of the original European Commission’s Expert Group on Violent Radicalisation (established 2006) and the subsequent European Network of Experts on Radicalisation (ENER). Since 2003, he has been coordinating research on terrorism and radicalisation, which has resulted in several publications. "Jihadi Terrorism and the Radicalisation Challenge. European and American Experiences" was published by Ashgate in 2011. This volume was included in the 2012 "Top 150 Books on Terrorism and Counterterrorism", established by the academic journal "Perspectives on Terrorism". His analysis on the impact of 9/11 on Europe was published in 2013 in a volume edited by Mohammed Ayoob and Etga Ugur of Michigan State University ("Europe: Reinforcing Existing Trends", in: "Assessing the War on Terror". Lynne Rienner, 2013, pp. 137–159). Recent studies on radicalisation and terrorism have been released by the Brussels-based Egmont Institute: "Returnees – Who are they, why are they (not) coming back and how should we deal with them ? Assessing policies on returning Foreign Terrorist Fighters in Belgium, Germany and the Netherlands" (with Thomas Renard, February 2018); "Anticipating the post-Daesh landscape" (October 2017); "‘All Radicalisation is Local’. The genesis and drawbacks of an elusive concept" (June 2016); "Facing the fourth foreign fighters wave. What drives Europeans to Syria, and to Islamic State? Insights from the Belgian case" (March 2016).