This study is a qualitative and quantitative analysis of written and spoken manifestos authored by lone offenders that planned to or committed a targeted attack (n = 30). The acts of violence were primarily motivated by an ideology or a personal grievance, and occurred between 1974–2021. The main objective of this retrospective study was to examine if a behavior-based threat assessment instrument, the Terrorist Radicalization Assessment Protocol (TRAP-18), could be applied to a thin slice of data using only language evidence compiled by the perpetrator before the event occurred. Findings indicate that 17 out of 18 TRAP-18 indicators (94%) were able to be coded in the manifestos. Proximal warning behaviors ranged from 2 to 7, with an average of 4.5. The average number of distal characteristics was 3.8 across the sample. The most frequent proximal warning behaviors were leakage, identification, fixation, and last resort. The most frequent distal characteristics were changes in thinking and emotion, framed by an ideology, and personal grievance and moral outrage. Further analyses of the manifestos comparing written versus spoken communications, ideologically based versus grievance-fueled attacks, and seven categories of primary motivations, supported the generalizability of the TRAP-18 when applied to only language data. A definition for targeted violence manifestos is proposed and examined within a genre framework. Application to threat assessment and management is discussed. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

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