Going Beyond Secrecy: Methodological Advances for Two-mode Temporal Criminal Networks with Social Network Analysis A thesis submitted to the University of Manchester for the degree of Doctor of Philosophy in the Faculty of Humanities 2016 Chiara Broccatelli School of Social Sciences 2 Contents List of Tables.............................................................................................................................. 6 List of Figures ............................................................................................................................ 6 List of Abbreviations.................................................................................................................. 7 Abstract ...................................................................................................................................... 8 Declaration ................................................................................................................................. 9 Copyright statement ................................................................................................................. 10 Acknowledgements .................................................................................................................. 11 PART I .................................................................................................................................... 12 Chapter 1 ................................................................................................................................ 13 Introduction: Is applying Social Network Analysis to Criminal Networks a good idea? ......................................................................................................................................... 13 1.1 Introduction ........................................................................................................................ 13 1.2 Social Network Analysis for Criminal Networks: the Origins .......................................... 14 1.3 Advances in applications of Social Networks Analysis to Covert Networks .................... 17 1.4 Criminal Network definition(s) .......................................................................................... 19 1.4.1 Covert networks, covert groups or covert organisations? ........................................... 21 1.5 Difficulties and Challenges in Analysing Covert Networks with SNA ............................. 24 1.6 How to Analyse Covert Networks? Building a Network Model ....................................... 26 1.6.1 Building a network model: the abstraction phase ....................................................... 27 1.6.2 Building a network model: the representation phase .................................................. 28 1.7 Why Longitudinal Two-Mode Networks? ......................................................................... 30 1.7.1 One-mode versus two-mode networks ........................................................................ 30 1.7.2 Static versus dynamic networks .................................................................................. 31 1.8 A Network Model for Analysing Covert Networks: a Recap ............................................ 34 1.9 Ethical Considerations ....................................................................................................... 35 1.10 Overview of the Thesis .................................................................................................... 35 Chapter 2 ................................................................................................................................ 38 Critical Review of SNA studies on Covert Networks .......................................................... 38 2.1 Introduction ........................................................................................................................ 38 2.2 Understanding the Nature of Covert Ties: Why Do People Interact Under Secrecy? ....... 39 2.3 Understanding the Nature of Covert Ties: How Do People Interact Under Secrecy? The Ambiguity in the field ....................................................................................................... 42 2.4 Literature Review of the SNA Contributions in the Field of Covert Networks................. 45 2.4.1 SNA as a metaphor ...................................................................................................... 46 2.4.2 Covert communication exchanges .............................................................................. 50 2.4.3 Co-participation in covert actions ............................................................................... 55 2.5 Critical Review of the Literature: a Recap ......................................................................... 60 2.6 Conclusions ........................................................................................................................ 63 PART II ................................................................................................................................... 67 Chapter 3 ................................................................................................................................ 68 The Bi-Dynamic Line-Graph ................................................................................................ 68 3.1 Introduction ........................................................................................................................ 68 3.2 The Duality between Individuals and Events .................................................................... 69 3.3 Temporal Proximity and Temporal Sequence Dimensions ............................................... 70 3.3.1 Temporal proximity .................................................................................................... 71 3.3.2 Temporal sequence ...................................................................................................... 72 3 3.4 Building a Bi-Dynamic Line-Graph .................................................................................. 73 3.4.1 Different nodes and different ties ................................................................................ 73 3.4.2 Line-graphs ................................................................................................................. 74 3.4.3 Three steps .................................................................................................................. 75 3.5 Bi-Dynamic Line-Graph Formal Definition ...................................................................... 83 3.5.1 Temporal proximity and temporal sequence in BDLG ............................................... 84 3.6 Two-Mode, One-Mode and Bi-Dynamic Line-Graph: a Comparison ............................... 85 3.7 Why are Bi-Dynamic Line-Graphs really necessary? ........................................................ 87 3.7.1 Advantages .................................................................................................................. 87 3.7.2 Disadvantages ............................................................................................................. 88 3.8 Bi-Dynamic Line-Graph for Covert Networks .................................................................. 89 3.9 Conclusions ........................................................................................................................ 91 Chapter 4 ................................................................................................................................ 92 Cohesion and Cohesive Subgroups in Two-mode Temporal Networks ............................ 92 4.1 Introduction ........................................................................................................................ 92 4.2 The Concept of Cohesion in SNA...................................................................................... 93 4.2.1 Measuring the network property of cohesion ............................................................. 93 4.3. The Notion of Cohesive Subgroups in SNA ..................................................................... 94 4.3.1 Measuring subgroup cohesion .................................................................................... 95 4.4 Some Challenges of Defining and Measuring Cohesion and Cohesive Subgroups .......... 96 4.5 Proposed Method for Detecting Cohesive Subgroups in Two-Mode Networks ............... 98 4.5.1 Measuring cohesion: bi-cliques detection ................................................................... 99 4.5.2 Moving beyond simple bi-cliques ............................................................................. 101 4.6 Analysis Bi-cliques: An Example .................................................................................... 103 4.6.1 Detecting bi-cliques in two-mode networks ............................................................. 103 4.6.2 Representing bi-cliques with the Bi-Dynamic Line-Graph ...................................... 105 4.6.3 The importance of the analysis of bi-cliques ............................................................ 106 4.7 Cohesion under Covertness .............................................................................................. 107 4.8 Cohesive Subgroups Under Covertness ........................................................................... 109 4.8.1 Examples of SNA contributions in analysing co-offending networks ...................... 112 4.8.2 The major problems