Data Selection

The following is an excerpt from the Method section of the full dissertation. The full spreadsheet of the data collection process can be found here: DISSERTATION FULL DATA COLLECTION.

There are a multitude of studies and online databases of mass shooters that could be used to define the shooters who could be included in the current study. However, due to the differences in accepted definition of mass shooting between various studies and databases, as well as the multiple criteria that are specific for the current study, it was determined that multiple data sources would be used and cross-referenced to ensure an exhaustive survey of young mass shooters.

Peter Langman’s online database for school shooters ( was the first place reviewed due to the overlap of this study’s population of young mass shooters and Langman’s focus on school shooters, the majority of whom are 25 and younger. provides the ability to filter by criteria of shooter’s age, country of attack, and number of victims. Additionally, has an online library that includes full texts of narrative accounts that are publicly available. Although not all of the included shooters for the current study were considered school shooters and included in Langman’s database, the majority of the full texts were found on this website (Langman, 2020).

The shooters found through the filtered search on were entered into an excel spreadsheet, along with the following important characteristics: year of incident, age, location of incident, number of victims (wounded, fatalities, and total), and if there is a known publicly available narrative. After compiling this list, the next databases reviewed were some of the most widely used: FBI Active Shooter Reports, NYPD Active Shooter Assessment Report , Mother Jones, and The Washington Post. Since these data sources did not have an option to filter by criteria, all distinct shooters from these databases were added into the excel spreadsheet database. Other reviewed databases that were mostly redundant were Lankford (2016) and Klarevas (2016). Finally, the extensive online crowdsource database Gun Violence Archive was used to capture potential shootings that met criteria for the current study but did not get the publicity or notice to be included in the other databases. Gun Violence Archive is a database that includes lists of every shooting incident reported in the United States since 2014 in which four or more people were wounded by gunfire. Gun Violence Archive has the ability to filter by perpetrator age, year of incident, and only includes shootings within the United States, so all shooters who were 25 or younger were included from Gun Violence Archive into the distinct shooter list spreadsheet. At the end of compiling the list of distinct mass shooters from these databases, there were a total of 801 potential shooters for the study.

The next phase of reviewing the data was to remove shooters who did not meet criteria based on age, removing 294 shooters for a remaining total of 507 shooters. After reviewing the remaining shooters there were two whose incidents occurred outside of the United States and they were removed, leaving 505 shooters. The review for victim criteria followed, which took the most time and was the point in which the remaining shooters who did not meet the study’s criteria were removed. Each shooting was reviewed via a Google search to review specifics about the incident with information verified from at least two different sources. Specifically, the number of people killed and wounded by bullets were distinguished from people injured in other ways (other types of weapons, falling, etc.), removing 58 shooters for a total of 447 possible shooters remaining. Additionally, descriptions of the incidents provided information that distinguished which incidents met the criteria of mass shooting as defined by the current study and from those that did not. Virtually all of the incidents added through Gun Violence Archive involved gang violence, gun fights (people shooting at one another), or shootings in private residences that were targeted (typically involving family or significant others), all of which do not meet the criteria for mass shooting defined by the study. When a shooter met all of the study’s criteria for mass shooting, a Google search was used to further scrutinize whether or not there existed a public narrative account. This involved searching the shooter’s name, the year of the shooting, and keywords that would indicate a narrative account: manifesto, letter, diary, journal, note, writing. There were some instances in which news articles reported the presence of a suicide note or letter to a family member left on the body of a shooter that were not made publicly available. In these instances, extensive research was conducted to find access to such documents. There was one instance in which there was a written account by a shooter that was determined by the researcher to not meet the criteria for a narrative account and was not included in the current study (Jared Loughner). After this extensive review, 433 shooters were removed and the complete list of 14 young mass shooters was finalized.