Complex networks and quantitative models of crime and terrorism
Network analysis can yield powerful insights into the latent structure of spatial and temporal data, as it is often the case with violent events (Yuan et al.
2019). Yet, as noted by Malcolm Sparrow in one of the earliest studies of crime and network analysis: “It would be enormously gratifying, therefore, if we could simply throw the existing network analysis toolkit at criminal intelligence databases, and come away with a set of valuable new insights. Of course it is not that easy” (Sparrow
1991). One of the main challenges of network-based studies of crime and terrorism is usually data incompleteness, dynamic behaviour (Gera et al.
2017) and the fact that “dark” networks tend to be covert and illegal (Bakker et al.,
2012; Raab and Milward
2003; Gerdes
2015), which makes the identification of key nodes and links more difficult than with other networks.
Despite potential “hidden” data limitations, network-based studies of crime and terrorism have rapidly expanded since the beginning of the 2000s due to the availability of new data sources and the development of complex networks and quantitative models. Spatial networks, which are usually constructed by connecting crimes and potential criminal’s address or connecting pairs of crimes (Oliveira et al.
2015) have helped identify crime pattern motifs (Davies and Marchione
2015), and have been used to predict crime, considering a street network (Rosser et al.
2017). The analysis of social networks has expanded to study organised crime networks, drug production (Malm et al.,
2008), cybercrime and extremist networks (Morselli
2013). Social networks have also been used to model the diffusion of fear of crime as a reaction to direct and indirect victimisation (Prieto Curiel and Bishop
2017), providing a potential explanation as to why fear of crime can increase even if crime rates are being reduced (Prieto Curiel and Bishop
2018).
Networks are also increasingly used to visualise, model and counter terrorist organisations (Bakker et al.,
2012; Krebs
2002; Carley
2006). The study of terrorist social networks usually looks at the network topology and identifies which actors are the most central (Everton
2009). Extant literature shows that terrorist organisations tend to find a balance between efficiency and security (Gerdes
2015; Morselli et al.,
2007). Centralised networks, such as the Provisional Irish Republican Army (IRA) in Northern Ireland, are theoretically more efficient than decentralised ones but also less resilient to external threats, while decentralised networks are more difficult to detect and disrupt but also much less efficient at communicating resources and orders (Chuang and D’Orsogna
2019; Price
2019).
Beyond the social dimension of terrorism, space is now recognised as a fundamental dimension of both criminal and terrorist networks (Radil
2019; Bahgat and Medina
2013; Medina and Hepner
2008). Space provides the physical framework upon which crime and terrorist attacks are conducted. It shapes the strategies of covert organisations by acting as a facilitating or constraining factor in their fight against government forces or civilian populations. Geographical distance plays a critical role, as attacks are frequently executed near important areas or the city centre (Savitch
2014). Therefore, a frequent approach in terrorism studies is to detect spatially dependent events and self-reinforcing hotspots (Bahgat and Medina
2013). This approach focuses on how different events are linked or how spatial proximity can influence the formation of social networks (Skillicorn et al.
2019).
Another approach is to use exponential random graph models to explore the spatial and social network causes of violence. In Africa, recent research using exponential random graph models suggests that rebel groups whose turfs overlap are more likely to fight each other (Cunningham and Everton
2017). Space can also enable criminal and terrorist organisation to spread geographically by using border regions as sanctuaries (Arsenault and Bacon
2015), as in the Lake Chad region today (Walther et al.,
2020).
Additional variables can be added to shed light on the social and spatial dynamics of terrorist networks, including ideology, tactics, weapons, targets and active regions (Gera et al.
2017; Campedelli et al.,
2019a,
b). A recent analysis of the terrorist attacks which occurred from 1997 to 2016 around the world shows, for instance, that groups with opposite ideologies can share very common behaviours (Campedelli et al.,
2019a,
b). In recent years, particular emphasis has been given to radical Islamist organisations, whose structure has been found to be resilient even if important social nodes were removed (Medina
2014). In West Africa, network studies have shown that Islamist organisations were capable of travelling long distances (Skillicorn et al.
2019), relied on a limited number of key brokers able to establish links with other rebel groups (Walther and Christopoulos
2015), and had a destabilising effect on regional political stability (Dorff et al.,
2020).
Internal structure and mobility patterns of Boko Haram
Boko Haram (which means “Western education is a sin”) is the name given by external observers to the organisation founded by Mohammed Yusuf in 2002. The organisation has used several different names since the Nigerian police killed Yusuf in Maiduguri in July 2009. From 2010 to March 2015 and from August 2016 onwards, the organisation led by Yusuf’s successor, Abubakar Shekau, was known as Jama‘at Ahl al-Sunna li-l-Da‘wa wa-l-Jihad (Group of the People of Sunnah for Preaching and Jihad). The organisation adopted the name Wilayat Gharb Ifriqiya (Islamic State in West in Africa Province, ISWAP) after it pledged allegiance to the Islamic State under the leadership of Shekau in March 2015. In August 2016, Islamic State announced that it had appointed Abu Mus’ab al-Barnawi as the new leader of ISWAP.
There is little agreement as to the organisational structure of Boko Haram. For some scholars, Boko Haram is a “centralized and nominally unified organization” in which Abubakar Shekau exercises a high degree of strategic and operational control (Zenn
2019). According to this perspective, Shekau’s ruthless leadership allowed him to build a strongly unified organisation in which opponents were either killed, expelled or forced to follow his orders. While not particularly effective in winning battles and holding territories, this centralised leadership was instrumental in limiting the number of splinter groups, with the exception of the short-lived group Ansar al-Muslimin fi Bilad al-Sudan, better known as Ansaru, founded in 2012 and largely dormant since 2013 (Zenn and Pieri
2018).
Another strand of literature argues that Boko Haram is “organised under a loose federation of operating cells under the broad umbrella headship of the Islamic standard ‘Shura Council’” , a consultative assembly (Anugwom
2019). According to this view, Boko Haram operates more as “a collection of loosely linked cells and bands than as a tightly disciplined hierarchical army” (Thurston
2017). For some authors (Weeraratne
2017), Boko Haram has adopted a “cell-like structure” since the execution of its leader Muhammad Yusuf in 2009. This structure, in which individual cells maintain little direct contact with the central leadership, allows local and regional commanders to enjoy a significant level of autonomy in their operations against governmental and civilian targets. The number of decentralised cells that composes Boko Haram, however, remains a matter of speculation. Local informants report that while Boko Haram is divided internally, “no one can pinpoint precisely how many these cells are and how far connected to the apex leadership these were” (Anugwom
2019). Fragmentation, however, has a cost as different cells might antagonise and compete against each other (Chuang and D’Orsogna
2019).
Boko Haram is known for its high mobility. Since it became violent in 2009, the organisation has been able to conduct an average of two attacks each day, taking on average the lives of nearly 11 people daily. The Boko Haram insurgency, which initially focused on cities, has mainly been active in rural areas since 2013, where it relies on cheap Chinese motorcycles to conduct its attacks (Agbiboa
2019). The move to rural areas has allowed Boko Haram to challenge the Nigerian military and to exploit agricultural and natural resources around Lake Chad. While Boko Haram had focused its attacks on northeastern Nigeria until 2014, increasing pressure from government forces and vigilante groups has led the terrorist organisation to conduct an increasing number of attacks in neighbouring Chad, Cameroon and Niger. Focusing on the organisation’s diffusion across the region, Dowd (Dowd
2017) shows, for example, that Boko Haram has contracted subnationally, suggesting that the organisation is relocating to neighbouring countries instead of expanding. The mobility patterns that sustain these attacks remain largely under-reported.
Thus far, the debate on the organisational structure and mobility of Boko Haram primarily relies on qualitative data collected through interviews with former members of the Jihadist organisation, evaluation of tactics, court transcript, letters written between Boko Haram commanders and other extremist organisations, and propaganda videos (Kassim and Nwankpa
2018). Studies using quantitative approaches to detect and describe the social networks and spatial patterns of Boko Haram have mainly focused on relationships between the organisation and its enemies rather than on its internal dynamics (Walther et al.,
2020). An exponential random graph model approach has shown that the emergence of Boko Haram in northern Nigeria led to an increase in the number of conflicts, even between pairs of actors that did not include Boko Haram (Dorff et al.,
2020). Finally, some attempts have been made to create a multi-layer network of Boko Haram based on open-source data that includes shared events, collaborations, membership and financial ties (Cunningham
2014). That network is extremely sparse due to its relatively young cell-like structure and its lack of collective leadership (Gera et al.
2017).
Due to the secretive nature of terrorist groups, the internal structure of Boko Haram and whether it is a centralised organisation is still unknown. Whether Boko Haram cells tend to operate locally or have a high degree of mobility also remains under-explored. And, in that vein, paths which are frequently travelled by Boko Haram members and whether international borders work as frictions to the group or as safety structures is still an open question with potential policy implications.