In Board of County Comm 'rs v. Brown, 520 U.S. 397 (1997), the United States Supreme Court expanded on the meaning of "policy" and "custom" and the logic behind the requirement that one be identified before liability is imposed: "Locating a "policy" ensures that a municipality is held liable only for those deprivations resulting from the decisions of its duly constituted legislative body or of those officials whose acts may fairly be said to be those of the municipality. Similarly, an act performed pursuant to a "custom" that has not been formally approved by an appropriate decisionmaker may fairly subject a municipality to liability on the theory that the relevant practice is so widespread as to have the force of law." Id. at 404 .