Since there have been only a few efforts to examine how the planning process affects the outcome of a terrorist plot, this research brief reports some preliminary findings from an analysis of the impact of the length of the planning process, the impact of multiple participants, and the volume of precursor activity on the success or failure of terrorist plots in the United States.
Data from the American Terrorism Study were used in this analysis. A total of 504 terrorism plots in the United States from 1980-2015 were analyzed to determine 1) whether the plot was successful, partially successful, or unsuccessful; 2) the total number of participants involved in the plot; 3) the number of known activities related to the planning or preparation of the planned terrorist event; and 4) the number of days from the first identified “preparatory” activity to the date of the planned terrorist incidents. The data pertained to 132 far-right terrorism plots, 84 far-left plots, 75 Islamist extremist plots, and 126 environmental extremist plots. The study found that terrorists who engaged in a significantly shorter planning and preparation cycle had the greatest probability of success. The greater the number of preparatory acts required for commission of a terrorist incident, the greater the probability of failure. Contrary to most expectations, the fewer the number of persons involved in the preparation process, the lower the rate of success. Multiple participants enabled the preparatory acts to be committed by several persons, which decreased the possibility that the precursor conduct would receive attention from law enforcement. 3 tables and 1 figure