Cato published a paper of mine today entitled “Terrorism and Immigration: A Risk Analysis.” I began this paper shortly after the San Bernardino terrorist attack in December last year when it became clear that few had attempted a terrorism risk analysis of immigration in general, let alone focusing on individual visa categories. There were few studies on the immigration status of terrorists and the vast majority of them were qualitative rather than quantitative. Inspired by the brilliant work of John Mueller and Mark Stewart, I decided to make my own.
From 1975 through the end of 2015, 154 foreign-born terrorists murdered 3024 people on U.S. soil. During that same time period, over 1.14 billion foreigners entered the United States legally or illegally. About 7.4 million foreigners entered the United States for each one who ended up being a terrorist. Startlingly, 98.6 percent of those 3024 victims were murdered on 9/11 (I did not count the terrorists as victims, obviously). However, not every terrorist is successful. Only 40 of those 154 foreign-born terrorists actually ended up killing anyone on U.S. soil.
Immigrants frequently enter the United States on one visa and adjust their status to another. Many tourists and other non-immigrants frequently enter legally and then fall out of status and become illegal immigrants. I focused on the visas foreigners used to enter the United States because applications for that visa are when security screenings are initially performed.