FBI sniper Lon Horiuchi shoots and kills Vicki Weaver during an 11-day siege at her home at Ruby Ridge, Idaho.

The Federal Bureau of Investigation (FBI) is the domestic intelligence and security service of the United States and its principal federal law enforcement agency. An agency of the United States Department of Justice, the FBI is a member of the U.S. Intelligence Community and reports to both the attorney general and the director of national intelligence. A leading American counterterrorism, counterintelligence, and criminal investigative organization, the FBI has jurisdiction over violations of more than 200 categories of federal crimes. The FBI maintains a list of its top 10 most wanted fugitives.

A sniper is a military or paramilitary marksman who engages targets from positions of concealment or at distances exceeding the target's detection capabilities. Snipers generally have specialized training and are equipped with telescopic sights. Modern snipers use high-precision rifles and high-magnification optics. They often also serve as scouts/observers feeding tactical information back to their units or command headquarters.

Lon Tomohisa Horiuchi is an American former Federal Bureau of Investigation (FBI) Hostage Rescue Team (HRT) sniper and former United States Army officer who was involved in the 1992 Ruby Ridge standoff and 1993 Waco siege. In 1997, Horiuchi was charged with manslaughter for killing Vicki Weaver at Ruby Ridge; the charges were later dropped due to Constitutional supremacy, granting federal officers immunity from actions taken in the scope of their practice.

The Ruby Ridge standoff was the siege of a cabin occupied by the Weaver family in Boundary County, Idaho, in August 1992. On August 21, deputies of the United States Marshals Service (USMS) came to arrest Randy Weaver under a bench warrant for his failure to appear on federal firearms charges after he was given the wrong court date. The charges stemmed from Weaver's sale of a sawed-off shotgun to an undercover federal informant, who had induced him to modify the firearm below the legal barrel length.