In Williams v. Superior Court (1993) 5 Cal. 4th 337 19 Cal. Rptr. 2d 882, 852 P.2d 377, the Supreme Court interpreted the scope of Public Records Act exemption for police investigative files. The court held that once an investigation has begun, all materials that relate to the investigation and are thus properly included in the file remain exempt from disclosure indefinitely. (Id. at pp. 355, 361-362.) Significantly, the court noted that the exemption "protects materials that, while not on their face exempt from disclosure, nevertheless become exempt through inclusion in an investigatory file." (Id. at p. 354.) Though the provisions of the Public Records Act are inapplicable to civil discovery proceedings (Gov. Code, 6260), the act's express exemption of police investigative files from disclosure reinforces the view that such files are confidential in nature. The Public Records Act (Gov. Code, 6250 et seq.) includes a specific exemption from disclosure for law enforcement investigative files. This exemption permits the state to withhold "records of . . . investigations conducted by, or records of intelligence information or security procedures of . . . any state or local police agency, or any such investigatory or security files compiled by any other state or local police agency . . . for correctional, law enforcement or licensing purposes . . . ." (Gov. Code, 6254, subd. (f).)