The Ariel Rios Federal Building was constructed in the early 1930s as part of the redevelopment of the Federal Triangle area. The Rios Building is located in the Federal Triangle in Washington, D.C., across 12th Street from the Old Post Office, which the new building was designed to replace. The New Post Office, as the Rios Building was originally known, housed the headquarters of the Post Office Department until that department was replaced by the United States Postal Service in 1971. The building, which now houses the headquarters of the U.S. Environmental Protection Agency, was renamed on February 5, 1985, in honor of Ariel Rios, an undercover special agent for the Bureau of Alcohol, Tobacco, Firearms and Explosives who was killed in the line of duty on December 2, 1982.