Playboy founder Hugh Hefner poses at the Playboy Mansion in the Holmby Hills. Picture: Kevork Djansezian/AP

New York - The FBI released the file it maintained on Playboy founder and editor-in-chief Hugh Hefner two years after the legendary publisher passed away - and it's revealing.

The bureau interviewed Hefner in the late 1950s and 1960s over what is described as "obscene material."

The file also contains a memo written to then-Director J Edgar Hoover in which the agent in charge pitches putting Hefner and his photographer Edward Oppman under surveillance to see if either was transporting "pornographic images" across state lines.

However, the investigation didn't turn up any crimes.

"Persons interviewed advised that Hefner too clever to violate Federal or local laws," the bureau's investigation concluded.

Hefner was later arrested in Chicago for publishing "obscene and suggestive" photos of Jayne Mansfield, but won a jury trial.

The file also contains news clippings from a case where Hefner won the right to mail Playboy to subscribers without breaking the law.