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Apportioning Culpability in Multiple Perpetrator Acts of Terrorism

Kate Y. O’Malley 1, James D. Seward 1, Michael Welner 1, *
1,* The Forensic Panel, 224 West 30th Street, New York City, New York, USA.


The Depravity Standard instrument was developed to operationalize depraved elements of crimes. It consists of 25 items that were derived using multiple sources of data, including case reviews, input from professionals, and over 40,000 survey respondents. This paper presents preliminary data on the use of the Depravity Standard in cases with multiple perpetrators, examining its efficacy in differentiating the culpability of co-conspirators in a terrorist act. The U.S. has been the site of three high-profile terrorist events with dual perpetrators: the 1995 Oklahoma City bombing by ex-U.S. Military acquaintances Timothy McVeigh and Terry Nichols; the 2013 Boston Marathon bombing by brothers Tamerlan and Dzhokhar Tsarnaev; and the 2015 San Bernardino mass shooting by husband and wife Syed Rizwan Farook and Tashfeen Malik.

In this pilot project, two independent raters applied the 25 items of the Depravity Standard to each of the six perpetrators to determine which of each pair was the more culpable. Interclass correlation coefficients revealed a high degree of agreement between the raters, attesting to the reliability of the Depravity Standard items. Examination of the total number of Depravity Standard items present reveals McVeigh was more culpable than Nichols. The other four perpetrators were similarly culpable to their partners. These current findings indicate that the Depravity Standard is a promising instrument to determine comparative culpability in terrorist actions with multiple perpetrators. Ongoing analyses of public participation data indicate some items to be more indicative of depravity than others, and future analyses will compare weighted scores.

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