Newly released FBI files show agents across the country and at the highest level of the agency investigated "Deep Throat" -- the 1972 porn movie, not the shadowy Watergate figure -- in a vain attempt to roll back what became a cultural shift toward more permissive entertainment.

The documents released to The Associated Press show the expanse of agents' investigation into the film: seizing copies of the movie, having negatives analyzed in labs and interviewing everyone from actors and producers to messengers who delivered reels to theaters.

All of it in a failed attempt to stop the spread of a movie that some saw as the victory of a cultural and sexual revolution and others saw as simply decadent.

"Today we can't imagine authorities at any level of government -- local, state or federal -- being involved in obscenity prosecutions of this kind," said Mark Weiner, a constitutional law professor and legal historian at Rutgers-Newark School of Law. "The story of 'Deep Throat' is the story of the last gasp of the forces lined up against the cultural and sexual revolution and it is the advent of the entry of pornography into the mainstream."

The papers are among 498 pages from the FBI file on Gerard Damiano, who directed the movie and died in October. Released this month following a Freedom of Information Act request by the AP, they are just a glimpse into Damiano's roughly 4,800-page file. More than 1,000 additional pages were withheld under FOIA exemptions and because they duplicated other material; the balance of the file has not yet been reviewed and released.

Many parts of the released files are whited out and the FBI's ultimate targets are unclear, but the seriousness with which the agency treated the investigation is unquestionable.

Authorities have long said the movie was made with mafia money -- and the FBI has linked the mob with porn over the years -- but the file includes no mention of mob links.

The file includes memos between the FBI's top men -- L. Patrick Gray, William Ruckelshaus and Clarence Kelley, successive heads of the agency after J. Edgar Hoover -- and field offices so widespread, it seemed nearly all of the country's biggest cities were involved.

While much of the probe centered in New York, where many involved in the film lived, and Miami, where it was largely shot, agents from Honolulu to Detroit were involved.

On various entries in the file, a checklist of top FBI brass appears in the top right corner, with initials next to some names. One of those listed is W. Mark Felt, the FBI second-in-command whose "Deep Throat" alias as a Watergate informant came from the movie's title. However, none of the markings indicate he read any of the materials on the movie whose name became synonymous with his role in bringing down Richard Nixon's presidency.

Felt got the double-entendre nickname because he leaked crucial information about Nixon administration corruption on "deep background" to Washington Post reporter Bob Woodward. His identity remained a secret until 2005. He died in December.

Aside from investigative records tracking subpoenas, interviews, screenings and shipments of the film, the Damiano file includes various FBI agents' play-by-play accounts of the movie's plot, and the specific role of Damiano in the agency's investigation.

The FBI notes Damiano had been "somewhat cooperative," On Aug. 7, 1973, an assistant U.S. attorney general writes to Kelley, saying Damiano is being considered for immunity. The memo doesn't specify the crime, though mentioned throughout the file is the charge of interstate transportation of obscene material.

Among the areas of the case file whited out is an interview with the star of the film, who at the time went by the name Linda Lovelace.

"Deep Throat" achieved fame unlike any pornographic film in history and become the most widely known adult film to reach a general audience. It was hugely profitable -- made for about $25,000 and amassing hundreds of millions in receipts -- and became a cultural buzzword.

Officials at every level of government tried to stop screenings and obscenity trials continued for years. But in the end, experts say, it represents the end of an era in which the government sought to stop the changing cultural tides.

Eugene Volokh, a law professor at UCLA, said the oddity of the scope of the investigation into "Deep Throat" is a reflection of very different times.

"Certainly today, with our broadly socially less restrictive attitude to most pornography and to sex more broadly it may seem odd that the government was spending so much effort on something like this," he said. "But attitudes back then were much different."