By The U.S. Federal Bureau of Investigation

In 2014, the FBI published its first report, A Study of Active Shooter Incidents Between 2000-2013, and subsequently published annual and bi-annual reports reflecting its continued research into active shooter incidents based on the FBI’s definition of an active shooter. Through its initial research, the FBI identified and reported on 305 active shooter incidents occurring in the United States between 2000-2019. It was later determined there were potentially other active shooter incidents fitting the FBI’s active shooter definition that had not previously been identified. …. As a result, the FBI evaluated and identified an additional 28 active shooter incidents that occurred between 2000 and 2019, bringing the total designated active shooter incidents during this time period to 333. … This valuable information is intended to assist law enforcement and the public in developing strategies to stop active shooter threats, prevent acts of violence, and prepare for, respond to, and recover from such incidents.

Washington, DC: FBI, 2021. 35p.

By U.S. Department of Homeland Security

An Active Shooter is an individual actively engaged in killing or attempting to kill people in a confined and populated area; in most cases, active shooters use firearms(s) and there is no pattern or method to their selection of victims. Active shooter situations are unpredictable and evolve quickly. Typically, the immediate deployment of law enforcement is required to stop the shooting and mitigate harm to victims. Because active shooter situations are often over within 10 to 15 minutes, before law enforcement arrives on the scene, individuals must be prepared both mentally and physically to deal with an active shooter situation.

Washington, DC: US Department of Homeland Security, 2008 13p.

By James Silver; Andre Simons; and Sarah Craun

"In 2017 there were 30 separate active shootings in the United States, the largest number ever recorded by the FBI during a one-year period. With so many attacks occurring, it can become easy to believe that nothing can stop an active shooter determined to commit violence. [...] Faced with so many tragedies, society routinely wrestles with a fundamental question: can anything be done to prevent attacks on our loved ones, our children, our schools, our churches, concerts, and communities? There is cause for hope because there is something that can be done. In the weeks and months before an attack, many active shooters engage in behaviors that may signal impending violence. While some of these behaviors are intentionally concealed, others are observable and -- if recognized and reported -- may lead to a disruption prior to an attack. Unfortunately, well-meaning bystanders (often friends and family members of the active shooter) may struggle to appropriately categorize the observed behavior as malevolent. [...] Once reported to law enforcement, those in authority may also struggle to decide how best to assess and intervene, particularly if no crime has yet been committed. By articulating the concrete, observable pre-attack behaviors of many active shooters, the FBI hopes to make these warning signs more visible and easily identifiable. This information is intended to be used not only by law enforcement officials, mental health care practitioners, and threat assessment professionals, but also by parents, friends, teachers, employers and anyone who suspects that a person is moving towards violence."

Washington, DC: U.S.. Federal Bureau of Investigation, 2018. 30p.