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The cast and producers of FX’s upcoming event series The People v. O.J. Simpson: American Crime Story visited the TV Critics Association press tour for a supersize hour-long panel. Cuba Gooding Jr., who plays O.J. Simpson, said shooting the series was “an emotional roller coaster.” “It was the hardest role I’ve ever played,” he added.

The series, based on Jeffrey Toobin’s book, The Run of His Life, was meticulously vetted for accuracy, according to executive producer and director Ryan Murphy. “I thought I knew everything about the case but I didn’t,” he said. “I’ve never worked on a project that had more legal vetting than this — at least five lawyers went over every line.”

Casting the ten-hour series was a long process. Multiple actors auditioned for each role, with the exception being Sarah Paulson, whom Murphy knew he wanted to play Marcia Clark. Murphy joked, “She had no choice.” For her part, Paulson wasn’t sure she could play the woman “who wasn’t cut out to be a public figure,” but, “if Ryan believes it, you tend to believe it. He’s been right before, so I tend to trust him.”

None of the actors contacted their real-life counterparts but they did watch a lot of video footage of the trial and any interviews they did at the time of the trial. “I’m me. He’s him. He’s iconic,” Courtney B. Vance said of playing Johnnie Cochran. “I’m going to do as much research as I can. I didn’t trap myself in the iconic figure Cochran was. I just wanted to keep the train rolling.”

David Schwimmer knew he wanted to play the role of Robert Kardashian when he learned Kardashian was the heart of the story. “Kris Jenner was very generous with her time and memories of Robert,” he said. “He was a very religious man who had a strong relationship with God. It helped me to understand his decisions at the time.” Gooding Jr. chose not to visit Simpson in prison where “he’s a shell of himself.” Gooding said he was playing the “charismatic, flamboyant, and braggadocious” 1994 O.J.

“I never had any doubt someone would make a great film on this subject,” Toobin said. “This story is one of the great American stories. This is a story of race, sex, violence, sports, and the only witness is a dog.”