The analysis of criminal and terrorist organisations as social network structures: a quasi-experimental study Efstathios D. Mainas European Police Office (Europol), Eisenhowerlaan 73, 2517 KK, The Hague, Netherlands. Email: efstathios.mainas@europol.europa.eu Submitted 1 April 2012; accepted 2 April 2012 Keywords: social network analysis, criminal networks, terrorist networks, quasi-experiments Efstathios D. Mainas, is a professional doc- torate student in criminal justice at the University of Portsmouth. He has extensive law enforce- ment and crime analysis experience, having worked for the Greek coastguard as an invest- igator and adviser since 1991, and the European Police Office (Europol) as a senior analyst since 2003. He holds two masters degrees in Police Science & Management and in Higher Education from the Universities of Portsmouth and Man- chester, respectively. He also has a diploma from the Hellenic Naval Academy and a bachelor’s degree in Business Administration & Manage- ment from the University of Piraeus. His main research interests are in social network analysis (SNA) applications against criminal and terrorist networks, organised crime and intelligence-led policing. Efstathios D. Mainas is the MSc Vathek Dissertation Prize winner for 2010 from the Insti- tute of Criminal Justice Studies, University of Portsmouth. ABSTRACT The need to tackle organised crime and terrorism threats indicates, among other things, the import- ance of analysing efficiently and effectively the patterns of criminal ties. Social network analysis (SNA) offers conceptual frameworks, techniques and software tools to measure and visualise empirical networks of any kind. The aim of this study was to test, examine and consider the usefulness of SNA as a principal approach for the analysis and investigation of criminal and terror- ist organisations. Two quasi-experiments were deployed, using a conceptual analytical frame- work consisting of topological, cohesive subgroups, centrality and key player measures, to see whether the application of network concepts and tech- niques can help law enforcement and intelligence agencies understand and derive meaning from complex and/or large data sets. The results con- firmed the research hypothesis and key conclu- sions were drawn. It was found that SNA is a quite effective and reliable approach that gives both investigators and analysts the power to know criminal and terrorist network structures. Clearly, SNA can influence a new way of thinking and improve professional practice through the develop- ment of intelligence-led applications. The study furthers understanding regarding the use of net- work concepts and techniques for crime analysis and investigation, and it can be used to inform decisions about SNA programmes and technologies. INTRODUCTION Catastrophic terrorism, as experienced by the attacks against the USA on 11 Sep- tember 2001 (9/11), points to terrorist evo- lution that was improbable a few decades International Journal of Police Science & Management Volume 14 Number 3 Page 264 International Journal of Police Science and Management, Vol. 14 No. 3, 2012, pp. 264–282. DOI: 10.1350/ijps.2012.14.3.285