It was the evening of April 14, 1865. The Civil War had ended and Washington was celebrating. President Abraham Lincoln entered the balcony at Ford's Theater to a standing ovation: a symbol of a return to normal life in America. 

The following morning the president was dead and assassin John Wilkes Booth became one of the most infamous figures in history.

But now, nearly 157 years since the single shot was fired, one man says he has evidence of "the most egregious fake news cover-up in American history."

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"What if I were to tell you that John Wilkes Booth did not fire the gun that killed President Lincoln?" independent researcher Paul Mellen asks.

Fox Nation's new special "Who Really Shot Abraham Lincoln?," based on Mellen's book of the same name, enlists retired U.S. Marshal Lenny DePaul to investigate the theory that might unravel history as we know it.

It all started with a pocket watch. Mellen, an avid collector, bought the gold piece in an online auction nine years ago. He discovered the watch belonged to Union Major Jonathan Ladd, who was believed to be at President Lincoln's bedside when he passed away on April 15, 1865, at 7:22 in the morning.

"I keep it set at 7:22," Mellen says, showing DePaul the watch. "I'm not a historian. I [didn't] know anything about the Lincoln assassination before I bought this watch."

Mellen began investigating the president's death, going down a rabbit hole of digitized police reports and witness testimony from the National Archives. Mellen concludes the evidence reveals a "secret shooter" and cover-up that stretches from Washington all the way to the Vatican.

"Does it make any sense for an actor, acting alone, to come to assassinate the president with a single shot Derringer?," Mellen asks. "The pistol only had one bullet."

In this March 17, 2015, file photo, John Wilkes Booth's pistol used to kill President Abraham Lincoln is displayed at a new exhibit at the Ford's Center for Education and Leadership.

In this March 17, 2015, file photo, John Wilkes Booth's pistol used to kill President Abraham Lincoln is displayed at a new exhibit at the Ford's Center for Education and Leadership. (AP Photo/Andrew Harnik, File)

Mellen sets the scene: An hour after Lincoln arrives at Ford's Theater, the play hits its climax and a bang rings through the building. Mayhem ensues as patrons ransack the president's balcony box looking for a piece of history. The pistol, however, was not discovered until hours later.

"You're telling me it's a contaminated crime scene," DePaul says.

"Everybody's on their hands and knees looking for souvenirs," Mellen responds. "Nobody finds the murder weapon?"

The gun was found by a man looking for his missing keys after helping move Lincoln's wounded body across the street. Instead of turning the pistol over to authorities, the patron gave it to a reporter.

"The cover-up is now in play," Mellen claims.

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Could Booth have been the fall guy in a much larger plot hatched by a secret Southern society and covered up by the Catholic Church?

DePaul goes on the hunt with historians and a firearms expert to find out who was really behind the murder of the century.

You can stream "Who Really Shot Abraham Lincoln?" on Fox Nation today. 

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