Watch America's Book of Secrets Season 2 in Australia

The notion of a universe inhabited by alien creatures can be found just about everywhere in American popular culture. But could mankind really have been visited by alien beings from other worlds? And might the truth have been kept secret for centuries? Ancient Astronaut theorists Erich von Daniken and Giorgio Tsoukalos, along with Apollo 14 astronaut Edgar Mitchell, journalists, scientists and government officials explore the mainstream resistance to the idea that aliens have been visiting the Earth for centuries. Has the United States government conspired with other nations to hide the facts about mankind's extraterrestrial past? Could there really be a global cover-up of ancient alien activity? One that shields the public from a profound knowledge that, if revealed, could shatter the very fabric of our civilization?

For decades, the criminal organization known as "The Mafia" has stained the fabric of American society. But what are the secrets behind the Mob's sinister success? According to the FBI, the American Mafia still has approximately 3,000 active members, and just like the iconic mobsters of the past, the modern Mafia's ill-gotten gains still come at a price: blood, bullets, and a massive body count. Uncover the secret world of organized crime and the violent tactics used by the Cosa Nostra to gain money and power. How did the Mafia become so powerful? How is it possible that with hundreds of gang related killings in Chicago in the 1920s, not one gangster--including the most violent of all, Al Capone--was ever convicted of murder? Why was the Director of the FBI, J. Edgar Hoover, reluctant to go after the Mafia in the 1930s and 40s? Could the Mafia's influence extend beyond local police and politicians? And what new illegal activities is the Mafia involved in today?

They are the original domestic terrorists, hiding underneath white hoods and flowing robes, and taking cover in the rights and freedoms that they are actively seeking to destroy. The Ku Klux Klan--although officially considered by the U.S. Government to be a racist organization--is not an illegal one. And while objectionable to most Americans, its philosophy of racial intolerance is protected as free speech under the First Amendment. But just how large, powerful, and dangerous is the Ku Klux Klan? This episode exposes the nearly 150 years of KKK history and the many attempts to discredit the Klan's demands for segregation and white supremacy. Johnny Lee Clary, once the Imperial Wizard of the White Knights of the Ku Klux Klan in Mississippi, shares inside knowledge of the Klan, including the secret handshakes, secret greetings, and the secret goals of the odern hate group.

They are secretly stalking America's streets and highways, hiding in plain sight and compelled by one simple motive: the thrill of taking another person's life. Since the 1970s, the United States has produced an estimated 1,400 serial killers--more than double the combined total of the rest of the world. What causes a seemingly normal human being to engage in serial acts of murder? This episode uncovers the psychological, biological and sociological make-up of these dangerous murderers. Why do they kill? How can they be identified and stopped before they strike? Former FBI profiler Clint Van Zandt, criminal psychologists Eric Hickey and Helen Morrison, journalists, scientists and law enforcement experts reveal the secret motives of serial killers like "BTK Killer" Dennis Rader and Jeffrey Dahmer--and explain why Ted Bundy, Donald Harvey "The Angel of Death" an the "Grim Sleeper" Lonnie Franklin Jr. were able to evade capture for years while they amassed a shocking number of victims.

The history of neo-Nazi groups in the United States is examined.

Uncovering the psychological allure of cults, their leaders and methods of controlling their members.

How much do we really know about what goes on behind the doors of the Oval Office?

Uncovering the conspiracies behind America's 40-year drug campaign and why marijuana is classified as equally dangerous as heroin.

Bigfoot is everywhere you look, but why are so many millions of Americans obsessed with this mysterious man-ape? This episode sheds new light on some of the nation's darkest Sasquatch secrets.

Over the last century there have been four successful presidential assassinations and a multitude of failed attempts. But do we know the real story behind these assassination plots?

American treasure hunters are convinced that there are missing fortunes scattered all around the country just waiting to be found.

Chronicling the history of the Hells Angels Motorcycle Club.