A Department of Homeland Security Center of Excellence led by the University of Maryland

Comparing Failed, Foiled, Completed and Successful Terrorist Attacks

Comparing Failed, Foiled, Completed and Successful Terrorist Attacks

Project Details


The current research provides a new database recording failed and foiled jihadist plots against the United States and selected overseas allies occurring between 1993 and 2017. The data are thus extensive in terms of time period covered and countries included. This report outlines some of the key findings, focusing on trends and case studies from the data collected. First, the attacks against the U.S. homeland are considered, both in terms of the nature of all attempts and in terms of the difference between those attacks that succeed and those that do not. Since the failed and foiled plots project also collected data on countries that are members of the European Union and the North Atlantic Treaty Organization as well as Australia and New Zealand, the second section of the report provides some international comparison of the threats emerging in recent years. This section takes the data from 2010, when there was a steep increase in threats to the United States, through 2016, the last complete year of data collection, to provide a general picture of the threat to the West and permit comparison between the United States and other western democracies. The analysis draws on work completed in the early years of the project with the development of a detailed coding framework and a test of the reliability of the coding scheme.

It is certainly the case that in the United States there are more jihadist plots that are successfully disrupted than terrorist attacks that can be said to have achieved some kinetic effect. How plots come to fail or to be foiled is therefore of great importance to the study of terrorism and to the development of counterterrorism policy. There can be no comprehensive picture of the threat without analyzing what violent jihadist adversaries planned to do as well as what they actually managed to accomplish. Examining failed and foiled plots is essential to understanding their intentions as well as their capabilities. Nor can the validity of public concern be judged without an evaluation of what extreme jihadists aspired to do. A balanced view of plots, successful and unsuccessful, is essential to public appreciation of the threat. The current data therefore allow an insight into the aspirations of those who target the United States and allied countries as well as an understanding of how plots came to fail or were successfully disrupted.

Primary Findings: 

Since the February 1993 bombing of the World Trade Center, there have been 121 jihadist-linked plots to use violence against the American homeland. Only 15 of these plots were completely successful, with an additional seven that were partially successful and partially foiled; one that was partially successful and partially failed; and two that contained elements of success, with further aspects of the attack that were both failed and foiled. The number of attempted and successful plots has increased in recent years, both in the United States and in the other countries studied, with a steep increase after 2010. However, most U.S. jihadist plots were completely or partially foiled (82%), and most of those foiled plots involve government surveillance and/or government informants who enter the plot at an early stage. Surveillance is also the most frequent route to disruption outside the United States. Despite the dominance of early government intervention, in 13 cases, community tip offs and in three cases, family tip offs, set the investigation in motion. Of the 16 cases that involved a failure of plans, six failed completely, three had elements of success, and seven also involved interventions that foiled the plot.


The dataset used in this project was constructed from public sources on successful, as well as failed and foiled, jihadist attempts to use violence against the homelands of the United States and its Western allies since the first bombing of the World Trade Center in 1993. These sources include not only news outlets but also government documents including Department of Justice and FBI statements. For U.K. cases, Crown Prosecution documents were also consulted. It is acknowledged that any data derived from public sources may omit information known only to intelligence agencies; however, such are the constraints for research in the public domain.


Project Period: 
July 2012 to December 2017