The 1 October After-Action Review, released in July 2019, gives an in-depth look at law enforcement response to the deadliest mass shooting in modern U.S. history. CJI was honored to work with the Las Vegas Metropolitan Police Department (LVMPD) on this exhaustive review of the 1 October mass-casualty shooting. The 93 recommendations outlined in this report (many of which have already been adopted by LVMPD) offer guidance for other departments on responding to mass casualty events.