Hamm and Spaaij constructed a database funded by the United States Department of Justice in which they identified 124 instances of lone wolf terrorist attacks in the United States between 1940 and 2016; the list includes "about" 30 planned attacks that are known not to have been carrier out, or that have been identified as FBI sting operations, or as hoaxes. Hamm and Spaaij defined lone wolf terrorism narrowly; they required an attacker to be politically motivated, this excluded, for example, mass shooters such as Adam Lanza, whose motive appeared to be entirely personal. And they had to have acted entirely alone, excluding cases like the 2015 San Bernardino attack carried out by a married couple, and the Boston Marathon bombing, carried out by a pair of brothers. The tightness of this definition was widely criticized.