"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."