Previous Article
News
Dutch Suspects of Terrorist Activity: A Study of Their Biographical Backgrounds Based on Primary Sources
European countries had and have to deal with a lot of terrorist attacks in the last couple of years. It is alarming that some of the most successful terrorist were already on the radar of the intelligence agencies. Predicting who will engage in terrorism is hampered by the absence of a typology of terrorists. Present and historic research agree that terrorists differ greatly in backgrounds, motivations and personality traits. In their article ‘Dutch Suspects of Terrorist Activity: A Study of Their Biographical Backgrounds Based on Primary Sources’ Maarten van Leyenhorst and Ada Andreas analyse the biographical backgrounds of clients of the Dutch Probation Service that have been suspected of terrorist activity.
Maarten van Leyenhorst is a former probation officer of the TER- team (Terrorism, Extremism and Radicalisation) within the Dutch Probation Service. Ada Andreas was involved in this special unit as a Senior Policy Advisor. The TER-team focusses on the risk-assessment of suspects and the supervision of terrorist offenders within the Dutch Probation Service. Both authors have years of experience working for this specialised unit. Their article is based on Maarten’s research for his thesis “Characteristics and Motivations of Dutch (suspected) Terrorists” (Van Leyenhorst, 2016). Their aim was to produce a structured overview of the biographical backgrounds of the suspected terrorists and contribute to the debate on the management of terrorist offenders.
Why is this research important?
Maarten van Leyenhorst: “There is more secondary research available than research based on primary resources. The Dutch Probation Service has a lot of information available about this group of offenders. It gives us a good insight in who we are dealing with.”
Ada Andreas: “There is not much information or research available about this target group yet. There is a lot we don’t know and that is why we need to continue to learn about and research this certain group of offenders.”
The research
By using primary-source data, this study adds new insights to existing information and historical findings. The authors had access to official police and prosecutor’s data. Information on certain characteristics and motivations of twenty-six Salafi-Jihadi clients were analysed.
Is it possible to identify a certain pathway these offenders go through?
Maarten van Leyenhorst: “Establishing pathways from from 26 files out of such a heterogenous group, has unfortunately not been possible. Also within our research sample, backgrounds and motivations differed greatly. You will need several hundreds of case files to determine overlapping trajectories. We did, however, find some overlapping.”
Ada Andreas: “It is difficult to identify a certain pathway. You also need to keep in mind that these pathways are changing when time passes as well. We see that the feeling of being part of a group is very important for them, but there is no recipe for a terrorist.”
What outcomes of the research you have done, were the most interesting?
Ada Andreas: “I thought that the roll of the family was very interesting. In many of the cases they warned the authorities, because they were afraid that their child was getting involved in terrorist activity. The response of authorities was often not very adequate. The result was that they did not get the help that was needed and lost their confidence in the authorities. This is something that needs to change. The prevention of radicalism is very important.”
Maarten van Leyenhorst: “I completely agree with Ada. We need to invest in facilitating gatekeepers and bystanders. Families are in the frontseat when it comes to identifying early radicalisation. For example, we identified that almost none of the offenders were raised according to strict Islamic guidelines. Despite the absence of a religious background, many families started to notice how their children started to impose strict religious guidelines in their families’ lives. It was furthermore noteworthy that the majority of the group grew up without a father being present and we were struck by the high presence of family relations, especially brothers and wives. We saw female extremists recurring in many files, but at the same time witnessed the inability to prosecute them successfully. Based on our experience, females conducted very specific tasks in the networks, such as recruiting and facilitating contact between terrorists. However, it has proven to be difficult to find enough legal evidence to convict females for terrorist activity.”
Future research
Will you continue to do research on this topic in the future?
Maarten van Leyenhorst: “I’m not a part of the TER-team anymore, but I am currently active as Trainer and Researcher at the Dutch Institute of Forensic Psychiatry & Psychology (NIFP) Here I am involved in two European Projects on violent extremism and I continue to do research on this topic.”
Ada Andreas: “For my master thesis I will continue to do more research on this topic. I will be looking at the different paths the offenders go through in their lives and I want to discover at what point they get involved with terrorist activity.
Are you interested in reading ‘Dutch Suspects of Terrorist Activity: A Study of Their Biographical Backgrounds Based on Primary Sources’? Please click on the link.

Related News
Keep up to date with the latest developments, stories, and updates on probation from across Europe and beyond. Find relevant news and insights shaping the field today.
Recap

Probation outside Europe
Governance Oversight and Accountability Mechanisms in Probation and Parole: Compare and Contrast Europe and USA
19/09/2025
Confederation of European Probation (CEP) and American Probation and Parole Association (APPA) organized an insightful webinar that introduced the theme “Governance oversight and accountability mechanisms in Probation and Parole. Compare and contrast Europe and USA”. This event took place on Thursday, 18 September 2025.
Recap

CEP Events, Framework Decisions
Recap: Expert Workshop on Framework Decision 2008/947/JHA and 2009/829/JHA
16/09/2025
The Expert Workshop held on September 10–11, 2025, in Brussels, Belgium, brought together senior managers, probation practitioners, criminal justice professionals such as lawyers and prosecutors from across Europe as well as representatives of the European Commission, Academy of European Law and European Judicial Network to discuss the advancements in the implementation of Framework Decisions 2008/947/JHA and 2009/829/JHA. Hosted at the Houses of Justice, the CEP Expert Workshop served as a dynamic platform for mutual learning, collaboration, and strategic planning.
New

Probation in Europe
New Vodcast Episode: Katharina Heitz on the Ressources-Risk-Inventory in Probation
11/09/2025
The 14th episode of Division_Y features Katharina Heitz, Head of the Central Department for Social Work at the Public Probation and Parole Service Baden-Württemberg, Germany.
Recap

CEP Board, Probation in Europe
CEP at ESC 2025: Penal Policy Transfer and Ageing in Prison in Focus
08/09/2025
The Confederation of European Probation (CEP) had a strong presence at the 25th Annual Conference of the European Society of Criminology (EUROCRIM 2025), held in Athens from 3 to 6 September 2025. As one of Europe’s largest gatherings of criminologists, the ESC annual conference brings together researchers, practitioners, and policymakers from around the world to exchange knowledge on crime, justice, and social responses. This year’s theme was “Logos of Crime and Punishment,” inspired by classical Greek philosophy.

Probation in Europe, Technology
Have Your Say: EU Call for Evidence on the Digitalisation of Justice (2025–2030)
18/08/2025
The European Commission has opened a Call for Evidence on the Digitalisation of Justice: 2025–2030 European Judicial Training Strategy.
Reading corner

Criminal Justice
Parole Futures
18/08/2025
At a time when many parole systems are experiencing considerable strain, the aims of this collection are twofold: first, to encourage systematic and critical reflection on the rationalities, institutions and practices of parole. Second, to think big, and pose ambitious ‘what if’ questions about the possible futures of parole and prison release. Offering novel insights from Asia, Australia, Europe, North America and South America, this collection builds the case for, and then showcases, a ‘way of doing’ parole research that is global in outlook, interdisciplinary in approach and unapologetically normative in character.
Subscribe to our bi-monthly email newsletter!
"*" indicates required fields
- Keep up to date with important probation developments and insights.