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

Education and Training

Launch of 40 e-Capsules: Training on EU Law for Justice Professionals

29/06/2026

The European Judicial Training Team of the European Commission is pleased to announce the launch of 40 e-capsules (each available in all EU languages) within civil law, criminal law and fundamental rights.

 

New

CEP

Delegation from Azerbaijan visits CEP Office in Utrecht

25/06/2026

On 23 June, a delegation from Azerbaijan visited the CEP office in Utrecht, the Netherlands. The delegation included representatives of the Probation Service, Ministry of Justice of the Republic of Azerbaijan, a judge of the Supreme Court of the Republic of Azerbaijan and representatives of the Embassy of the Republic of Azerbaijan in the Netherlands. The visit to the CEP office was part of a broader learning programme with Reclassering Nederland.

New

CEP

Newsletter June 2026 out now

25/06/2026

CEP’s latest newsletter is out now! It includes:

  • Recap of the Workshop on Caseload and Workload
  • Save the date: Workshop on Technology and Alternatives to Detention
  • New publications and outputs from Expert Groups
  • Call for a new Expert Group on Overcrowding and Net-Widening
  • Call for participation in DG training
  • and much more!

. >> Read here

>>Read previous newsletters

New

CEP, Directors General Meetings

CEP Call for Applications – Training Opportunity for Directors General 

24/06/2026

CEP is seeking 7 applications for an upcoming training programme, CEP Leadership Excellence Training, designed for a small group of Directors General or Deputy Directors General representing CEP member organisations. This training will take place on 19-21 October 2026, Zagreb, Croatia.

 

Probation Journal

Framework Decisions

Exploratory Study on the possible Lisbonisation of ex-third pillar acquis in the area of mutual recognition in criminal matters published

23/06/2026

Commissioned by the European Commission’s Directorate-General for Justice and Consumers (DG JUST) and undertaken by ICF SA in December 2023, the study, published in April 2026, assesses the mutual recognition of criminal decisions and cross-border cooperation on criminal matters.  

New

Probation in Europe, Probation outside Europe

New Division episode: Aditya Weriansyah about Probation, Prison and the work of NGOs in Criminal Justice in Indonesia

23/06/2026

The 21st episode of Division_Y features Aditya Weriansyah from Jakarta, Indonesia.

Subscribe to our bi-monthly email newsletter!