The CIA is often credited with 'advice' on Hollywood films, but no one is truly sure about the extent of its shadowy involvement. Matthew Alford and Robbie Graham investigate

Everyone who watches films knows about Hollywood's fascination with spies. From Hitchcock's postwar espionage thrillers, through cold war tales such as Torn Curtain, into the paranoid 1970s when the CIA came to be seen as an agency out of control in films such as Three Days of the Condor, and right to the present, with the Bourne trilogy and Ridley Scott's forthcoming Body of Lies, film-makers have always wanted to get in bed with spies. What's less widely known is how much the spies have wanted to get in bed with the film-makers. In fact, the story of the CIA's involvement in Hollywood is a tale of deception and subversion that would seem improbable if it were put on screen.

The model for this is the defence department's "open" but barely publicised relationship with Hollywood. The Pentagon, for decades, has offered film-makers advice, manpower and even hardware - including aircraft carriers and state-of-the-art helicopters. All it asks for in exchange is that the US armed forces are made to look good. So in a previous Scott film, Black Hawk Down, a character based on a real-life soldier who had also been a child rapist lost that part of his backstory when he came to the screen.

No matter how seemingly craven Hollywood's behaviour towards the US armed forces has seemed, it has at least happened within the public domain. That cannot be said for the CIA's dealings with the movie business. Not until 1996 did the CIA announce, with little fanfare, that it had established an Entertainment Liaison Office, which would collaborate in a strictly advisory capacity with film-makers. Heading up the office was Chase Brandon, who had served for 25 years in the agency's elite clandestine services division, as an undercover operations officer. A PR man he isn't, though he does have Hollywood connections: he's a cousin of Tommy Lee Jones.

But the past 12 years of semi-acknowledged collaboration were preceded by decades in which the CIA maintained a deep-rooted but invisible influence of Hollywood. How could it be otherwise? As the former CIA man Bob Baer - whose books on his time with the agency were the basis for Syriana - told us: "All these people that run studios - they go to Washington, they hang around with senators, they hang around with CIA directors, and everybody's on board."

There is documentary evidence for his claims. Luigi Luraschi was the head of foreign and domestic censorship for Paramount in the early 1950s. And, it was recently discovered, he was also working for the CIA, sending in reports about how film censorship was being employed to boost the image of the US in movies that would be seen abroad. Luraschi's reports also revealed that he had persuaded several film-makers to plant "negroes" who were "well-dressed" in their movies, to counter Soviet propaganda about poor race relations in the States. The Soviet version was rather nearer the truth.

Luraschi's activities were merely the tip of the iceberg. Graham Greene, for example, disowned the 1958 adapatation of his Vietnam-set novel The Quiet American, describing it as a "propaganda film for America". In the title role, Audie Murphy played not Greene's dangerously ambiguous figure - whose belief in the justice of American foreign policy allows him to ignore the appalling consequences of his actions - but a simple hero. The cynical British journalist, played by Michael Redgrave, is instead the man whose moral compass has gone awry. Greene's American had been based in part on the legendary CIA operative in Vietnam, Colonel Edward Lansdale. How apt, then, that it should have been Lansdale who persuaded director Joseph Mankewiecz to change the script to suit his own ends.

The CIA didn't just offer guidance to film-makers, however. It even offered money. In 1950, the agency bought the rights to George Orwell's Animal Farm, and then funded the 1954 British animated version of the film. Its involvement had long been rumoured, but only in the past decade have those rumours been substantiated, and the tale of the CIA's role told in Daniel Leab's book Orwell Subverted.

The most common way for the CIA to exert influence in Hollywood nowadays is not through anything as direct as funding, or rewriting scripts, but offering to help with matters of verisimilitude. That is done by having serving or former CIA agents acting as advisers on the film, though some might wonder whether there is ever really such a thing a "former agent". As ex-CIA agent Lindsay Moran, the author of Blowing My Cover, has noted, the CIA often calls on former officers to perform tasks for their old employer.

So it was no problem for CBS to secure official help when making its 2001 TV series The Agency (it was even written by a former agent). Langley was equally helpful to the novelist Tom Clancy, who was invited to CIA headquarters after the publication of The Hunt for Red October, an invitation that was regularly repeated. Consequently, when Clancy's The Sum of All Fears was filmed in 2002, the agency was happy to bring its makers to Langley for a personal tour of headquarters, and to offer access to agency analysts for star Ben Affleck. When filming began, Brandon was on set to advise - a role he repeated during the filming of glamorous television series Alias.

The former agent Milt Beardon took the advisory role on two less action-packed attempts at espionage stories: Robert De Niro's The Good Shepherd from 2006, which told an approximate version of the story of the famed CIA head of counter-espionage, James Jesus Angleton; and Charlie Wilson's War, the story of US covert efforts to supply the Afghan mujahideen with weaponry during the Soviet occupation of the 80s. In reality, this was a story that ended badly, as the Afghan freedom fighters helped give birth to the terrorists of al-Qaida. In the movie, however, that was not the case. As Beardon - who had been the CIA man responsible for the weapons reaching the Afghans - observed shortly before the movie came out, the film would "put aside the notion that because we did that [supply arms], we had 9/11".

Beardon's remark provides a clue to the real reason the CIA likes to offer advice to Hollywood, a clue that was expanded on by Paul Kelbaugh, the former associate general counsel to the CIA - a very senior figure in Langley. In 2007, Kelbaugh spoke at Lynchburg College of Law in Virginia - where he had become an associate professor - about the CIA's relationship with Hollywood. A journalist present at the lecture (who now wishes to be anonymous) reported that Kelbaugh spoke about the 2003 Al Pacino/Colin Farrell vehicle The Recruit. A CIA agent had been on set as a "consultant" throughout the shoot, he said; his real job, however, was to misdirect the film-makers. "We didn't want Hollywood getting too close to the truth," the journalist quoted Kelbaugh as saying.

Peculiarly, though, in a strongly worded email to us, Kelbaugh emphatically denied having said such a thing, and said he remembered "very specific discussions with senior [CIA] management that no one was ever to misrepresent to affect [film] content - EVER." The journalist stands by the original report, and Kelbaugh has refused to discuss the matter further.

So, altering scripts, financing films, suppressing the truth - it's worrying enough. But there are cases where some believe the CIA's activities in Hollywood have gone further - far enough, in fact, to be the stuff of movies. In June 1997, the screenwriter Gary DeVore was working on the screenplay for his directorial debut. It was to be an action movie set against the backdrop of the US invasion of Panama in 1989, which led to the overthrow of dictator Manuel Noriega. According to his wife, Wendy, DeVore had been talking to an old friend - the CIA's Chase Brandon - about Noriega's regime and US counternarcotic programmes in Latin America. Wendy told CNN: "He had been very disturbed over some of the things that he had been finding in his research. He was researching the United States invasion of Panama, because he was setting the actual story that he was writing against this; and the overthrow of Noriega and the enormous amounts of money laundering in the Panamanian banks, also our own government's money laundering."

At the end of that month, DeVore had been in Santa Fe, New Mexico, working on another project. He was travelling back to California when, at 1.15am on June 28, he called Wendy, a call she says has been excised from phone records. She told CNN she was "terribly alarmed" because he was speaking as though he were under duress. She was sure "someone was in the car with him". That was the last time Wendy DeVore heard from her husband.

A year passed, but the case refused to die and speculation mounted. Even the Los Angeles Times began contemplating CIA involvement. DeVore was presumed dead, but there was no body, and no end to the questions. Lo and behold, just nine days after the LA Times reported the case, DeVore's body was found, decomposing in his Ford Explorer, in 12 feet of water in the California Aqueduct below the Antelope Valley Freeway, south of Palmdale - a city located in "aerospace valley", so dubbed by locals for its reputation as a US military-industrial-complex stronghold - fuel to the fire for conspiracy theorists.

The coroner went on to declare the cause and manner of DeVore's death to be "unknown", but police eventually reached the tentative conclusion that the screenwriter's death was an accident: he had fallen asleep at the wheel, they said, before careening off the highway and into the water, where he drowned. But loose ends remain: DeVore's laptop computer containing his unfinished script was missing from his vehicle, as was the gun he customarily carried on long trips; after his disappearance, a CIA representative allegedly showed up at DeVore's house to request access to his computer; Hollywood private investigator Don Crutchfield noted that previous drafts of DeVore's script were inexplicably wiped from said computer during the same timeframe; police claimed that DeVore's vehicle careened off the highway, yet DeVore's widow was troubled by the absence of visible damage to the guardrail at the scene of the alleged accident; and how come no one noticed an SUV sitting in the water beneath a busy highway for a whole year? Perhaps the whole incident is too like a conspiracy movie to be a real conspiracy - but many remain troubled by De Vore's death.

Despite the CIA's professed desire to be more open about the role it plays in Holly-wood, it's hard to take its newfound transparency too seriously. After all, what use is a covert agency that does not act covertly, even if some of its activities are public? And if it is still not open about the truth of events decades ago, many of which have spilled into the public domain accidently, how can we be sure it is telling the truth about its activities now? The spy may have come in from the cold, but he still finds shelter in the dark of the cinema.

• Body of Lies is released next Friday