beachdeath:

In 1950, the FBI, charged with the responsibility of supplying the Civil Service Commission with background information on employees and applicants, took the initiative of establishing liaison with police departments throughout the country. Not content with acting only on requests to screen particular individuals, it adopted a preventive strategy that justified widespread surveillance. 

The FBI sought out friendly vice squad officers who supplied arrest records on morals charges, regardless of whether convictions had ensued. Regional FBI offices gathered data on gay bars, compiled lists of other places frequented by homosexuals, and clipped press articles that provided information about the gay world. Friendship with a known homosexual or lesbian subjected anyone to investigation. 

The Post Office, exploiting its authority to prevent the dissemination of obscene material through the mails, joined the antihomosexual campaign. The department established a watch on the recipients of physique magazines and other forms of gay male erotica. Postal inspectors subscribed to pen pal clubs, initiated correspondence with men whom they believed might be homosexual, and, if their suspicions were confirmed, placed tracers on victims’ mail in order to locate other homosexuals.

– John D’Emilio, Sexual Politics, Sexual Communities: The Making of a Homosexual Minority in the United States, 1940-1970