Genocide scholars use different models in order to explain and predict the onset of mass killing events.
"[13] Other terms used by several authors to describe mass killings of non-combattents include: In the United States, the Investigative Assistance for Violent Crimes Act of 2012, passed in the aftermath of the Sandy Hook Elementary School shooting in Newtown, Connecticut, clarified the statutory authority for federal law enforcement agencies to provide investigatory assistance to the States, and mandated across federal agencies, including the Departments of Justice and Homeland Security, a definition of "mass killing" as three or more killings during an incident, while making no reference to the choice of weapon.
[13] About why it occurs,[34] Valentino states that ideology, paranoia, and racism can shape leaders' beliefs for why genocide and mass killing may be justified.
[37] Manus Midlarsky also focuses on leaders' decision making but his case selection and general conclusions are different from Valentino's.
Both Midlarsky and Valentino mainly focus on proximate conditions, while Mann considers genocide within the broad context of ideologies and nation-states development.
According to Harff, these data are not necessarily the most accurate for a given country, since some sources are general genocide scholars and not experts on local history.