Writer and director Brett Morgan says what happened outside the 1968 Democratic convention was a pivotal moment in US history.
"In a decade of incredible spectacles, this was probably the spectacle of the 1960s," he says.
The story of the confrontation between anti-war demonstrators and baton wielding police officers in Chicago in August 1968 has been told again and again. However Morgen says there is a timeless quality to the story. The confrontation between establishment power and a mass popular movement keeps playing out across the world.
"The audience can really project their own story onto the screen. So when I've screened this film overseas, people have asked me, 'Were you thinking about Tiananmen Square, when you made this? Were you thinking about Seattle?'"
Morgen says he wanted to find a fresh way of telling the story, so in a way he went back in time.
He searched for archive film, and found a treasure trove.
There were more than 150 hours of 16mm film shot around the demonstrations. He got film from TV stations, and from ordinary people. Morgen found sometimes many people had filmed in the same places, providing different angles on key events.
"It's as if we have 50 cameras in the field," he says. "And we spent three years collecting all this media and really what we have been able to do 40 years after the events is reconstruct them in a way that nobody has ever seen." He also found hours of interviews with the defendants in the conspiracy trial of protest leaders. Here's Abbie Hoffman giving his thoughts on being tried.
At one point in the film Abbie Hoffman is asked what he thinks about the trial.
"Well, I have a good seat, and it's unbelievable theater, a great show. The outcomes don't look good, but the beginning and the middle is looking great," he says.
Morgen also had the transcript of the federal conspiracy trial. As he read he came across another confrontation as an 84 year old judge tried to control the wild and mouthy defendants.
"The trial provides a lot of comic relief, if you will, from the angst and the chaos and the horrors that the archival footage presents," Morgen says.
But he had no film of the trial. Cameras weren't allowed in the courtroom. Morgen then recalled a comment by one of the other defendants, Jerry Rubin.
"He referred to the trial as a cartoon show as many of the defendants did throughout the trial. It seemed like a really fun way of bringing this trial to light," Morgen says.
Morgan shows the trial used a motion capture animation technique developed for the film "Polar Express." It creates very life-like three dimensional animated characters.
A lot of the sequences depict Rubin, Hoffman, and the others making fun of their situation. One morning Hoffman and Rubin turned up in judicial robes, much to the annoyance of the judge.
"Take off those robes," the judge orders.
"Off with the robes?" says Hoffman. Courtroom observers then roar with laughter as the defendants unzip their black garments to reveal police uniforms underneath.
But it wasn't all fun. During the trial defendant Bobby Seale, chairman of the Black Panther Party, loudly demanded access to his own lawyer. The judge ordered US marshals to eject him. Morgen shows how they later carried Seale back into the courtroom bound and gagged to keep him quiet.
"It's as shocking today as it was at the time to see the chairman of the Black Panthers chained and gagged in a courtroom for simply trying to exercise his constitutional rights," said the film's director Brett Morgan.
Ultimately jurors acquitted the defendants of all conspiracy charges.
However, the judge imprisoned what had become known as the Chicago 8 for contempt of court, and he did the same to their lawyers. That's why Morgen called the movie "Chicago 10."
Brett Morgan said if there is a lesson to be learned from Chicago for this summer's Republican National Convention in St. Paul, it's that people must be allowed to protest.
"Whether it's outside the convention or a few blocks away or what have you, as long as they [protests] are honored," he said. "And we understand that every American has a right to protest and to try to silence that dissent is really unAmerican."
Brett Morgen said working on "Chicago 10" has made him confront the strength of his own beliefs and convictions.