Who was really behind the 9/11 terrorist attacks on New York? Was it the US government, meaning the Twin Towers were subject to a controlled explosion? Was it a Jewish conspiracy, with some claiming that Jews did not go to work in the World Trade Center that day? An exhibition titled "Conspiracy theories — then and now" at the Dalheim Monastery shows how such beliefs emerge and are maintained.

In the so-called "Protocols of the Elders of Zion," 12 Jewish leaders allegedly layed out their plans to conquer the world in writing. In reality, the 1903 document (pictured here in the exhibition at the Dalheim Monastery) is a work of fiction by Sergej Nilus, an anti-Semitic Russian writer and publisher. The protocols are a central part of modern day anti-Semitic conspiracy theories.

The idea of a Jewish conspiracy was also a central part of Nazi ideology. The Nazis spread alleged revelations gleaned from the fake Protocols of the Elders of Zion for their own purposes, reprinting them in their weekly "Der Stürmer" (The Attacker) propaganda newspaper.

People who believe in the barcode conspiracy probably have a special pen in their pockets when they approach a checkout counter to neutralize what they believe is negative energy radiating from the barcode. The barcode information supposedly aims to reduce the world population. Some companies even go so far as to print a line through the barcode to keep their customers happy.

Those seeking to explain major political events and revolutions have often invoked grand conspiracies. In the wake of the 1789 French Revolution, secret societies such as the Freemasons and Illuminati were seen as the all-powerful rabble-rousers. Pictured is an Illuminati Minerval class medal currently on show at the "Conspiracy Theory - Past and Present" exhibit that runs through March 22, 2030.

The assassination of US President John F. Kennedy has been the subject of conspiracy theories since the moment it took place on November 22, 1963, at the height of the Cold War. While many movies have tackled those theories, this one by Oliver Stone, which considers an alternative conclusion to the FBI's official story of a lone assassination, drew in more than $40 million in box office receipts.

Perhaps the largest scandal in US history, the Watergate affair that took down President Richard Nixon is captured in Oliver Stone's biographical picture, "Nixon." How could a break-in at an office building in 1972 lead to the US President's impeachment? Through the FBI's investigation, the president's role in the burglary and a tape-recording system in his offices was uncovered.

This political thriller is based on the book written by the two "Washington Post" reporters, Bob Woodward (Robert Redford, right) and Carl Bernstein (Dustin Hoffman (left), who uncovered President Nixon's role in the Watergate scandal. Their reporting, based on information from an FBI informant they referred to as Deep Throat, led to Nixon's resignation in 1974.

Based on the true story of a 1975 shootout that killed a tribal council member on South Dakota's Pine Ridge Reservation, "Thunderheart" dramatizes the story of a man with Sioux Indian roots, Ray Levoi (Val Kilmer), who moves to the reservation to investigate. Over the course of the investigation, the agent begins to reject the tactics of his fellow FBI agents.

Frank Sinatra stars in the 1962 original, "The Manchurian Candidate," in which a former POW is brainwashed into becoming an international assassin. The 2004 remake, featuring Denzel Washington, put a contemporary twist on the plot by setting the film during the Gulf War. The thriller takes on a major political tone as it questions the role of fictional corporations in US politics.

The Cold War has long proved a fertile backdrop for Hollywood. Based on a John le Carré novel, the 2011 thriller is set in London in the early 1970s and follows a retired spy in his search to uncover a Soviet agent who has infiltrated the British spy services, MI6. The espionage film stars Gary Oldman (left) and John Hurt (right).

Taking a more humorous approach to scandalous politics is "Wag the Dog," with Dustin Hoffman (l.) as a spin doctor who concocts a war with Albania in order to save the fictional US President, Robert De Niro (r.), from a sex scandal. The ploy is uncovered by William H. Macy, a suspicious FBI agent. Released in 1997, the film was seen as a tragic commentary on the role the media plays in politics.

Director Michael Moore is known for his outspoken politics. In the 1995 comedy, "Canadian Bacon," he imagines what would happen if the US invaded Canada. The biting message has that the US President has done so to boost the economy and his own approval rating. It was the last movie released with John Candy (right) in a starring role.