By Mark Kennedy, Entertainment Writer

NEW YORK (AP) --

What was to become the Broadway phenomenon "Hamilton" was still raw and unshaped when documentary filmmaker Alex Horwitz turned on his camera three years ago.

Whether Lin-Manuel Miranda's vision of Founding Father Alexander Hamilton would become a concept album or a musical or something else had yet to be determined. Horwitz didn't mind. He just wanted to be there beside Miranda.

"My take was 'I don't care what it ends up being. I just find it so compelling. Let me follow you as you continue to develop it,'" said Horwitz. "It was designed from the beginning to be a companion piece to 'Hamilton,' whatever that became."

Horwitz ended up being, quite literally, in the room when it happened. His documentary "Hamilton's America " debuts Friday on PBS as part of its Great Performances series, offering a behind-the-scenes look at the musical's creation and putting it in historical context.

The documentary maker, who befriended Miranda in college, didn't want to make a film about the making of the hip-hop-flavored musical. That had already been done with "Chasing Broadway Dreams," about Miranda's previous success with "In the Heights."

"I thought that this could be about history seen through Lin's eyes. That was the conceit of the film from the beginning," said Horwitz. "It's a sort of audio-visual liner notes that exists for all time now about this amazing, whirlwind experience he had."

Miranda allowed Horwitz extraordinary access, including a sequence in which he was captured composing the song "My Shot" while visiting Aaron Burr's home. Their friendship meant a level of comfort another filmmaker might not have gotten.

"He's much smarter than me," said Miranda, "so he said, 'Can I just start filming you writing your next thing?' in 2012, before we even knew this was a show. And the result is that he's got this great film."

The RadicalMedia documentary combines backstage footage with field trips to places key to "Hamilton," like actor Christopher Jackson, who plays George Washington, visiting Mount Vernon, and Leslie Odom Jr. who plays Aaron Burr, stopping by the Museum of Finance.

The film is also augmented by interviews with politicians and celebrities including President Barack Obama, former President George W. Bush, Speaker of the House Paul Ryan, Sen. Elizabeth Warren, former Treasury Secretaries Hank Paulson and Timothy Geithner, Questlove, Jimmy Fallon, John Weidman, Nas and Stephen Sondheim.

"It is quite a motley crew in the best possible way. Where else are you going to get a film that stars Questlove and Hank Paulson?" asked Horwitz. "People returned my calls because of 'Hamilton.'"

Horwitz is the perfect man for the job. His father, director and writer Murray Horwitz, won a Tony Award in 1978 for "Ain't Misbehavin'" and his mother is a classically trained opera singer.

He was a researcher for visionary director Julie Taymor and became an experienced film editor for RadicalMedia, having cut Joe Berlinger's documentary "Whitey," and is a big fan of Ken Burns. He also wrote and directed the zombie short film "Alice Jacobs is Dead."

"It's in my blood. I am a musical nerd. I am a history nerd," he said. "I wanted this movie to scratch both those itches for me and everyone in the audience as well."

Horwitz had about 100 hours of footage that he boiled down to 84 minutes. He hopes it appeals to both "Hamilton" fans and newcomers to the show.

"I know that this film is not the work that 'Hamilton' is. This film is a shadow of that far greater piece, in my mind," he said. "But if I did half as good a job as a documentarian as Lin did as a composer, then I think it will at least be an entertaining and enlightening piece of material and a worthy companion piece."

Associated Press writer John Carucci contributed to this report.

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