The Federal Bureau of Investigation (FBI) defines serial killing as "a series of two or more murders, committed as separate events, usually, but not always, by one offender acting alone". In 2005, the FBI hosted a multi-disciplinary symposium in San Antonio, Texas, which brought together 135 experts on serial murder from a variety of fields and specialties with the goal of identifying the commonalities of knowledge regarding serial murder. The group also settled on a definition of serial murder which FBI investigators widely accept as their standard: "The unlawful killing of two or more victims by the same offender(s) in separate events". The definition does not consider the motivation for killing nor define a cooling-off period.