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More plot participants, greater rate of attack success

New study examines how the planning process affects the outcome of a terrorist plot

The more people involved in planning a terrorist attack in the United States, the more likely it is to be successful, according to a new study by the National Consortium for the Study of Terrorism and Responses to Terrorism (START). However, the greater the number of preparatory acts required, the greater the probability for failure.

Using data from the American Terrorism Study (ATS) at the Terrorism Research Center at the University of Arkansas, researchers evaluated the relationship between success of plots and the number of participants and preparatory acts and the length of the planning process.

Among the preliminary findings:

  • Plots where known preparatory behaviors were limited to the three-week period prior to the incident had an 83.3 percent chance of being successfully completed.
  • Incidents with two or fewer known preparatory activities were successful 68 percent of the time, compared to a 23.5 percent success rate if the group or individual engaged in more than 10 preparatory acts.
  • Half of the plots with one participant were successful, compared to 60 percent of the plots with two or three participants and 73 percent of the plots with four or more participants.

The findings are explored in “Temporal Sequencing, Incident Sophistication, and Terrorist Outcomes” research brief, by Brent Smith, Jeff Gruenewald, Brent Klein, Katie Ratcliff, Summer Jackson and Ian Brecht. The research was supported by the Department of Homeland Security.


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