The case of the Frankfurt Airport attack in 2011 in which a 21-year-old man shot several U.S. soldiers, murdering 2 U.S. airmen and severely wounding 2 others, is assessed with the Terrorist Radicalization Assessment Protocol (TRAP-18). The study is based on an extensive qualitative analysis of investigation and court files focusing on the complex interconnection among offender personality, specific opportunity structures, and social contexts. The role of distal psychological factors and proximal warning behaviors in the run up to the deed are discussed. Although in this case the proximal behaviors of fixation on a cause and identification as a "soldier" for the cause developed over years, we observed only a very brief and accelerated pathway toward the violent act. This represents an important change in the demands placed upon threat assessors.

The Terrorist Radicalization Protocol 18 (TRAP-18) is tested on a sample of 80 people who were convicted for Islamist activities in Germany between 2006 and 2017. In the study, perpetrators of terrorist attacks will be compared to persons who have been convicted of propagandistic and financial terrorist support and of joining a terrorist organization abroad. Statistical analysis of the results shows that there are significant differences between terrorist perpetrators and persons convicted of nonviolent Islamist activities, both in the number of TRAP-18 items and in the proximal warning behaviors "pathway," "last resort," "energy burst," and "novel aggression." Subsequent ROC analyses underline both the specificity and sensitivity of the instrument. AUC values range from .83 to .90 for the four different models (TRAP-18 and the warning behavior typology as weighted and unweighted models). The highest discrimination between Islamist attackers and the non-attackers is achieved by the weighted warning behavior typology. The values for sensitivity (se = .80), specificity (sp = .93), positive predictive value (p+ = .80), and negative predictive value (p− = .93) are extremely promising. Public Significance StatementThe study deals with the question of whether TRAP-18 is capable of distinguishing persons who have committed an Islamist act of violence from those who have taken on more supportive, nonviolent roles in the scene. The results show that this is the case. Specific behavioral patterns can be identified that are overly coincidentally common in violent terrorists. Likewise, terrorists show more warning behavior than those who have not committed a violent crime. Against this empirical background, TRAP-18 has proven to be an instrument with a high potential for successful early detection of Islamist-terrorist violence.

The case of 24-year-old Anis A. who killed 12 and injured more than 50 people during a terror attack is analyzed from a threat assessment perspective. On December, 19th, 2016, the perpetrator drove a truck into a Christmas market in Berlin. The study is based on a qualitative analysis of investigation reports and open source media data. It traces the perpetrator's psychological and social history of radicalization, as well as the role of five proximal warning behaviors that occurred before and correlated with the attack: leakage, fixation, identification, last resort, and pathway. Data show that security authorities had an enormous amount of information on the perpetrator before the attack. Eventually security agencies presumed that no acute threat from Anis A. existed a month before the attack. It will become increasingly important in the future that officials fall back on evidence-based and validated evaluation criteria. It is for this reason that both the development and implementation of structured risk and threat assessment instruments, as well as the scientific debate about them, are highly desirable.

No abstract

No abstract