There's a true American saga on screens this weekend.

Twelve Years a Slave tells the story of Solomon Northup. He was an African-American musician from New York — a free man, until he was kidnapped in Washington, D.C., and sold into slavery. After an unlikely rescue from a Louisiana cotton plantation, he returned home and wrote a memoir, first published 160 years ago.

But the end of Northup's story is an unsolved mystery that has confounded historians for years.

A Story Brought To Life

Northup was drugged, kidnapped and sold into slavery not far from the National Mall in 1841. What is now the Federal Aviation Administration headquarters was once the site of "a slave pen within the very shadow of the Capitol," as Northup described it in his book, which he dictated to writer David Wilson.

Carol Wilson (no relation to David Wilson), a history professor at Maryland's Washington College, has studied hundreds of documented kidnappings of African-Americans before the Civil War. She says Northup's story is unique.

"First of all, that he could spend over a decade in slavery and then still get out — but also that he wrote an account, and it's really one of the most valuable narratives of a slave that we have because he experienced slavery as a free person," she says.

This kind of documentation is rare, says John Ridley, who wrote and produced the new film adaptation of Twelve Years a Slave.

"Even though we think we've seen every slave narrative, the reality is that very few of these stories have really ever been told and brought to life," he says.

The film is a visceral portrayal of the brutality of slavery — so is the book.

"When he's being whipped, you feel it. When he triumphs over something, or pulls a fast one on his owner, you're there with him, too," says Clifford Brown, who teaches at Union College in New York and has co-authored the new biography Solomon Northup: The Complete Story of the Author ofTwelve Years a Slave.

He says Northup's return home in 1853 made headlines. His memoir was published later that year.

His Final Request

After the book came out, Northup hit the lecture circuit, produced two unsuccessful stage plays about his experience and sued his kidnappers. There is also some evidence that he helped fugitive slaves escape through the Underground Railroad.

But by the end of the Civil War, Northup had disappeared from the public record.

"We know where his son is buried. We know where his father is buried. But we don't know where he's buried. It's a mystery," Brown says.

Brown and his co-authors, David Fiske and Rachel Seligman, have tried to solve that mystery for almost two decades. They've visited graveyards and combed through old death notices. They've even spoken with Northup's descendants, including Clayton Adams, Northup's great-great-great-grandson.

Adams shared a copy of Northup's book with his wife, India, when they were dating.

"I told her, 'I have this one book here that was very interesting and based on a true story,' " he says. After a few days, Adams' wife finished the book — and then learned that she was dating one of the author's descendants.

"I think I was just in awe that I knew someone that could actually have their history documented, which unfortunately, a lot of African-Americans don't have," India says.

Adams says he wishes he knew how the story of Northup ended. "It still is open. It's not closed," he says.

Adams describes reading the last words of Northup's book as heartbreaking; "I hope henceforward to lead an upright though lowly life, and rest at last in the church yard where my father sleeps," Northup wrote.

"So after all of that ordeal, his last request in his book, the last line is that he just wished when he dies he could lay right next to the grave of his father," Adams says.

He says the line still haunts him "every time I read it or think about it."

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