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Across the Universe? A Comparative Analysis of Violent Behavior and Radicalization Across Three Offender Types with Implications for Criminal Justice Training and Education


Authors: John G Horgan et. al.

Date of Publication: June 2016

Journal / Publisher: National Criminal Justice Reference Service


Purpose of the study

Key questions 

Differences between lone wolf terrorists and mass murderers

Design of the study


Using a series of bivariate and multivariate statistical analyses, the study compared demographic, psychological and offense-related behavioral variables across and between 71 lone actor terrorists and 115 solo mass murderers.

Number of participants




Type of ‘participant’ 

Lone actor


Understanding the differences between lone terrorists and mass murderers

Key findings 

There is little to distinguish these offender types in terms of their socio-demographic profiles. However, their behaviors significantly differ with regards to (a) the degree to which they interact with co-conspirators (b) their antecedent event behaviors and (c) the degree to which they leak information prior to the attack. 

The fundamental distinction between the two groups – motivation – dictates different actuation points for violence. Mass murderers do not engage in the decision and search activity involving calculations based on current political and security climates that characterize the incipiency of lone actor and solo actor terrorist attacks. A majority of mass murderers have feelings of being wronged by a particular person and target that person; others have grievances against a category of persons and target that category or act spontaneously against random targets.

In terms of group-related activities, the results indicate that lone actor terrorists were significantly more likely to try to recruit others, interact face-to-face with members of a wider network, virtually interact with members of a wider network, produce letters and/or public statements prior to the attack and recently join a wider movement. In terms of antecedent attack behaviors, lone actor terrorists were significantly more likely to have university experience, military experience, combat experience, criminal convictions, experience a tipping point in their pathway to violent extremism, change address prior to their attack, live alone, be socially isolated, engage in dry runs, demonstrate that their anger is escalating and possess a stockpile of weapons.

The vast majority of lone actor terrorists each demonstrated elements concerning: 

  1. Their grievance; 
  2. An escalation in their intent to act; 
  3. gaining capability – both psychologically and technically; and 
  4. attack planning.

Scripts for lone actor terrorists, solo terrorists (less preparation) and mass murderers are included.

Key recommendations 

Both offenders (lone wolf terrorist, mass murderer) are very similar in terms of their behaviors – this in turn suggests that similar threat and risk assessment. 

Phases may be identifiable on the trajectory into violence process, from grievance formation to fixation to capacity building to attack planning. If an individual is identified ahead of time (say for example after leaking key information), the individual’s position in this pathway can be plotted, and a range of disruption/prevention tools can be implemented from there. Traditional methods employed against formal terrorist organizations and loosely connected terrorist networks (such as counter-intelligence, HUMINT, interception of communications, surveillance of persons, targeted killing etc.) may not be as readily applicable against the threat of lone actor terrorists. Strategies aimed at countering radicalization in the community may have no reference point in identifying lone at-risk individuals. Deterrence measures also may prove problematic for countering lone actor terrorism. Because prediction and identification are difficult, it might be better to instead guard against future lone actor terrorists by making the actual undertaking of a terrorist attack more difficult. For example, it might be easier and more cost-efficient to deter a budding lone actor terrorist by making it more difficult to acquire the necessary bomb-making materials than by convincing him/her of counter-narratives.

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