Social network analysis (criminology)

Social network analysis in criminology views social relationships in terms of network theory, consisting of nodes (representing individual actors within the network) and ties (which represent relationships between the individuals, such as offender movement, co-offenders, crime groups, etc.) These networks are often depicted in a social network diagram, where nodes are represented as points and ties are represented as lines.
Key concepts.
Graph theory.
Centrality measures are used to determine the relative importance of a vertex or node within the overall network (i.e. how influential a person is within a criminal network, or, for locations, how important an area is to criminal behaviors). There are four main centrality measures used in criminology network analysis: 
Co-offenders.
"Legitimate strengths in criminal networks"
This article is a study of "...how legitimate world actors contribute to structuring a criminal network... [and] also underscores the facilitating role that some participants have in criminal settings". The basis of Morselli and Giguere's article is from a case study of an illegal drug importation network, monitored by law-enforcement over a period of two years. Their findings were that "...a minority of these actors were critical to the network in two ways: (1) they were active in bringing other participants (including traffickers) into the network; and (2) they were influential directors of relationships with both non-traffickers and traffickers."
"Networks of Collaborating Criminals: Assessing the Structural Vulnerability of Drug Markets"
This article analyzes an illicit drugs commodity chain which requires identifying the collaborating actors who are located within activity niches that link the raw materials to the market absorption, either through retail or consumption. "...uncovering the structure of connections among individuals involved in criminal enterprise will contribute to our understanding of how illicit markets function. In turn, this will lead to policy directives aimed at key pressure points to maximize crime prevention efforts". The created network should capture the roles, functions, and structures of the groups involved in the illicit drug commodity chain and reveal the links in the supply chain (i.e. source, supply, sales, and feeders). Using the created network the resiliency is determined by assessing the clusters in subgroups, identifying pivotal individuals holding central positions, and quantifying the potential to disrupt commodity and information flow by identifying the specific nodes to be removed for maximum effect. This study has three hypothesis: "Hypothesis 1: Individuals involved in production and transporting...will exhibit high small-world properties...Hypothesis 2: those involved in supplying drugs will be characterized by both small-world and scale-free properties as suppliers tend to belong to loosely organized clusters of people...with a few highly connected individuals – hubs. Hypothesis 3: Networked individuals involved in sales will be characterized by high small-world properties."
The application of social network analysis during the collaboration between criminals and terrorists when both use smuggling tunnels was explored by Lichtenwald and Perri. Lichtenwald and Perri referenced many of the notable scholars and key papers in the field.
Offender movement.
"Magnetic Facilities: Identifying the convergence Settings of Juvenile Delinquents"
Magnetic facilities refer to the attractiveness of a location for deviant behavior. This study looked at the self-nominated hangouts of 5,082 delinquent youth living in Southern California. The structure of these networks remained relatively constant over the time the study was conducted. The centrality statistics used were in-degree and betweenness to identify facilities operating as stable regional convergence locations. "Explaining the linkage between urban planning and crime patterns, Brantingham argues that four factors – accessibility through high-volume transportation conduits, placement, juxtaposition, and the operation of facilities – can account for the criminogenic capacity of specific places". Of the locations included in the network, the top twenty with the highest in-degree centrality scores in both the valued and dichotomous networks were investigated for the following three characteristics: facility type – coded as public space, freestanding building, attached or terrace style structure, or mall facility; place type – coded as movies, video store, fast food restaurant, shopping, outdoor recreation, school, and other; and school accessibility – counting the number of schools within a 5-mile radius of the property.
"Examining Juvenile Delinquency within Activity Space: Building a Context for Offender Travel Patterns"
This study looked at 2,563 delinquent youths in Southern California and assumed that crime locations were within the offenders activity space. The highlight of the study is the "...need to infuse a place-oriented approach to studying journey-to-crime". An individual’s behavior is influenced by numerous factors, of which spatial awareness emerges from the routine travel to and from activity nodes (i.e. work, school, shopping, and recreation sites). "Recent efforts to enhance journey-to-crime research: examine intraurban criminal migration using travel demand models; explore spatial-temporal constraints posed by routine activities; investigate how co-offending dynamics impact target selection; describe the journey away from crime sites; scrutinize subgroup variation; and assess the utility of distance decay models". Using the crime prevention theory (CPT), it asserts that offenders operate within their familiar settings which are learned as the delinquent travels between activity nodes along constant paths.