Skip to content

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.

New

Alternatives to pre-trial detention, Community Sanctions and Measures, Framework Decisions, Technology

Future of Criminal Justice: CEP’s Contribution to Key 2025 Dialogues

27/01/2026

Throughout 2025, CEP and its representatives actively participated in the online Technical meetings ahead of the HLF as well as the High Level Forum on Future of Criminal Justice taking place on 4-5 March 2025, 20-21 May 2025 and 1-2 October 2025 in Brussels, Belgium.

Recap

Alternatives to pre-trial detention

Recap: Webinar on Alternatives to Detention 2026

26/01/2026

On Thursday 22 January, CEP hosted the first webinar of 2025 on the topic of Alternatives to Detention. The session led by Ms. Marina Pajoni from the French Prison and Probation Service titled „Problem Solving Justice in Pracitce: The Meuse Probation Service´s Approach to Drug Addiction“ introduced an innovative programme developed by the Meuse Probation Service in close cooperation with the French Ministry of Justice.

New

Education and Training

CEP launches an interactive European map of probation education and training institution contacts

22/01/2026

The CEP is pleased to inform its members that a new dedicated section has been developed on the CEP website featuring an interactive map of Europe.

New

CEP Events

CEP activity calendar 2026

20/01/2026

As we begin the new year, we would like to thank all CEP members, partners, and participants for your continued engagement and valuable contributions. Your involvement plays an essential role in shaping CEP’s work and activities.

We are pleased to share the CEP calendar for 2026, which provides an overview of the events planned for the year ahead. We look forward to continuing our collaboration and welcoming you to upcoming CEP activities throughout the year.

Thank you for being part of the CEP community.

New

CEP members, Gender-based violence

Interventions Alliance’s Eden House Recognized as Outstanding

15/01/2026

CEP is delighted to share that Eden House, an Interventions Alliance residential service for women with high-risk or complex needs on probation, has been rated “Outstanding” overall by HM Inspectorate of Probation. In 2022, Eden House was honored with the CEP Public Protection Award. Our sincere congratulations to the team for this remarkable achievement.

 

New

Education and Training

The Judicial Training Dashboard

14/01/2026

The European Training Platform (ETP) is a search tool for justice professionals. You can find self-learning materials on a great variety of EU law practice areas and related topics, as well as links to training providers’ homepages and course catalogues.

Subscribe to our bi-monthly email newsletter!