EXCLUSIVE: 'Killing Reagan' Stars Reveal the High Level of Authenticity that Was Maintained on Set

ET was first on the set of the TV movie based on Bill O'Reilly's best-selling book.

ET was first on the set of the TV movie Killing Reagan, based on Bill O'Reilly's best-selling book, getting stars Tim Matheson and Cynthia Nixon to open up about their experience recreating the attempted assassination of former President Ronald Reagan.

Matheson plays President Reagan and Nixon embodies his wife Nancy Reagan in the chilling docudrama, which concentrates on the events of March 30, 1981. It was on that fateful day that John Hinckley, Jr., the 25-year-old son of a wealthy oil executive, stepped out of a crowd outside the Hilton Hotel in Washington, D.C., and opened fire with a six-shot revolver as the president left a speaking engagement.

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The shooting left Reagan seriously injured by a ricocheting bullet while a police officer and Secret Service agent were also struck by gunfire. Press secretary James Brady sustained the worst injuries as a bullet struck him in the forehead, leaving him partially paralyzed and with slurred speech. Brady was a leading voice for gun control in the U.S. until his death last year from injuries sustained in the 1981 assassination attempt.

Many of the actors are old enough to remember the incident, and they were able to recall the emotion they felt at the time thanks to director Rod Lurie's dedication to authenticity.

"Rod and the entire crew has created such a sense of reality," Matheson told ET. "Everybody calls me Mr. President."

Matheson revealed that Lurie also did not want him to meet Kyle S. More, the actor playing John Hinckley, Jr., prior to shooting the assassination scene to make the experience closer to the real thing.

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"He told me, '[They] never met, so [Reagan] never knew the face in the crowd when the assassination attempt happened,'" Matheson said.

Hinckley was found not guilty by reason of insanity in 1982 and ordered to undergo treatment at St. Elizabeth's Hospital in Washington, D.C. It was determined that the assassination attempt was an attempt to win the affections of actress Jodie Foster, whom he had written love letters to while she was studying at Yale University.

"By sacrificing my freedom and possibly my life, I hope to change your mind about me," Hinckley wrote to Foster, according to reports at the time. "This letter is being written an hour before I leave for the Hilton Hotel."

Hinckley was diagnosed with schizotypal and narcissistic personality disorders.

Now 35 years later, the would-be assassin has been granted full-time release from St. Elizabeth's Hospital. Judge Paul L. Friedman delivered the ruling Wednesday, allowing Hinckley, 61, to go home to his mother in Williamsburg, Virginia, no sooner than Aug. 5.

Reagan's daughter, Patti Davis, responded to the ruling in an emotional open letter.

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"I'm not surprised by this latest development, but my heart is sickened," Davis wrote on her website. "When my father was lying in a hospital bed recovering from the gunshots that nearly killed him, he said, 'I know my ability to heal depends on my willingness to forgive John Hinckley.' I too believe in forgiveness. But forgiving someone in your heart doesn't mean that you let them loose in Virginia to pursue whatever dark agendas they may still hold dear."

ET spoke to Foster in 1983, a year after Hinckley's sentencing, where she opened up about violence in America.

"I'm not a politician and it's not my point to make any political things. The only thing I can say from a very personal point of view is that we all know there are more violent and more bizarre crimes here than any place in the world except for say a country at war," Foster said at the time. "Things like this don't happen everywhere else."

The two-time Oscar winner went on to describe how her "brush with death" changed her.

"You do become very realistic about death -- what the idea of shooting means," Foster said. "About how many calories are spent going like this {moves finger like a trigger} ... You don't stab them. You don't touch them, and suddenly by this little tiny thing you've made this incredible imprint, and you've taken a life, and the idea that it takes so little to cause so much is pretty incredible."

Killing Reagan is set to debut on National Geographic Channel this fall.