Mary Jo Kopechne was 28 years old when she attended a party on Chappaquiddick Island, a tiny spit near Martha’s Vineyard, on July 18, 1969. Joined by five of her friends from the 1968 presidential campaign for Sen. Robert F. Kennedy, Kopechne had already made waves in Democratic circles in Washington, working for a Florida senator before moving to Kennedy’s Senate staff. She proved herself adept by helping to write an anti-Vietnam War speech for RFK, and helped write the address announcing his ill-fated candidacy for president.

Edward “Ted” Kennedy, meanwhile, was the last surviving son of Joseph Kennedy at the time of the party. After the wartime death of Joseph Jr. and the assassinations of John and Robert, Ted remained as the political leader of the family, a sitting U.S. senator from Massachusetts, with a potential run at the presidency in his future.

As the host of the party in question, Ted brought the women together for a reunion that included Kennedy’s cousin, Joseph Gargan, and former U.S. Attorney for Massachusetts Paul Markham. But by the end of the night, the festivities had turned tragic: Kennedy’s car overturned on a small bridge and landed upside-down in the water. While Kennedy survived, Kopechne, his passenger, drowned. What happened on that bridge? Was Kennedy drinking and driving? What were he and Kopechne doing together alone in the first place? The details at the time were, as they are now, sparse. It would be a full 10 hours before Kennedy reported the incident to local police.

It’s the story of this night that would become an enduring black mark on Kennedy’s political career and that serves as fodder for the new film Chappaquiddick, starring Jason Clarke as Ted Kennedy. The scandal haunted him, and the Democratic party, for decades and was also blamed for ruining his presidential prospects. (Kennedy for his part claimed in his autobiography that “it was not a determinant” in his decision to run for president in 1980.)

Screenwriters Taylor Allen and Andrew Logan felt the drama was the perfect subject for a film about the disposability of women, the impossible expectations of the Kennedy family, how power gets abused, and the role of the media in hiding or exposing political scandal.

Although they don’t claim complete veracity for their film—director John Curran says he wasn’t interested in making a documentary on the incident—all three men strove to hew as closely as possible to actual events. Logan and Allen based their script on the nearly 1000-page inquest released by the Massachusetts Supreme Judicial Court in 1970.

“The two people who really know what happened that night are dead: Ted and Mary Jo,” Curran says. “And the others around them, the ones that are still alive, they aren’t going to say anything.”

Part of the reason details are so spotty comes from those 10 hours of waiting to report the accident. Why didn’t Kennedy contact authorities sooner? He would later claim he was suffering from physical and emotional shock, and not thinking clearly. And then there was talk of a cover-up, of Kennedy and his press team attempting to downplay the incident so as not to harm his future political aspirations.

“Sometimes I’d like to scream a lot but I’m trying to hold it back,” said Gwen Kopechne, the mother of Mary Jo, to the Boston Globe. “It would be nice if somebody spoke up.” But she also told McCall’s Magazine that she believed Kennedy had been behaving erratically after the accident due to shock and a minor concussion. What she didn’t understand were how Gargan and Markham, Kennedy’s aides who also attempted to retrieve Mary Jo from the car after the accident, didn’t report the accident or force Ted to do so.

“Gargan and Markham not only failed to get immediate help, but also let the senator swim back alone to report the accident from Edgartown,” the elder Kopechne said. “This is the big hurt, the nightmare we have to live with for the rest of our lives: that Mary Jo was left in the water for nine hours. She didn’t belong there.”

No one ever provided the answers she wanted. In the immediate aftermath of the car accident, the nation—and the media—were largely distracted by the Apollo 11 moon landing.

“It was the greatest moment in John F. Kennedy’s presidential [legacy] happening at the worst possible moment for Ted-Kennedy-the-senator’s potential legacy,” Allen says. That backdrop of an already distracted news media provided Ted’s team with time for damage control, and further obscured the truth about what actually happened.

But once the moon landing receded from the immediate news cycle, the story of Kennedy and Kopechne exploded. Curran and his producers attempted to capture the media coverage by intercutting archival news footage and newspaper headlines throughout the narrative. The film also emphasizes the strain it put on Kennedy’s wife, Joan, who was pregnant at the time. She ultimately suffered a miscarriage, which she blamed on the incident. At the same time, she told the wire service United Press International, “I believe everything Ted said.” She didn’t pay heed to allegations that Kennedy and Kopechne were going for a midnight swim when the accident happened.

This fervor for more details about what exactly happened, and whether some misconduct had occurred between the married men and single women the night of the party, was also experienced by those who attended the party the night of Kopechne’s death. Among them were Susan Tannenbaum, who also worked on Robert Kennedy’s campaign staff.

“You can’t begin to understand what it’s been like,” Tannenbaum later said. “I place a tremendous value on the right of privacy, but suddenly I’m infamous. The real meaning of what you are and what you value remains intact inside yourself; but there you are splashed all over the papers. How would you feel if a reporter called your mother at 8 a.m. and asked whether she approved of her daughter’s conduct in spending the night with a group of married men?”

That aspect of the accident particularly galled the screenwriters. In an era when women were only beginning to enter the workforce in high numbers, press coverage only added to their objectification. “[Kopechne] was an intelligent, strong woman who worked for the Bobby Kennedy campaign in a high capacity and did really great work, including transcribing and then adding to the speech he gave about Vietnam,” Allen says.

In the end, Kennedy appeared in court and pleaded guilty to a charge of leaving the scene of an accident. Judge James Boyle sentenced Kennedy to the minimum punishment for the offense, two months’ incarceration, but Kennedy never served the jail time, as the judge suspended the sentence.

“He has already been and will continue to be punished far beyond anything this court can impose—the ends of justice would be satisfied by the imposition of the minimum jail sentence and the suspension of that sentence, assuming the defendant accepts the suspension,” Boyle said, with the result that the suspension was accepted by the defense team.

No public inquest into the death occurred, and Kennedy went on to make a televised speech about the accident. That speech is one of the few scenes in which the writers of Chappaquiddick took liberties with the facts of the case. In the movie, Kennedy cousin Joe Gargan unsuccessfully tries to convince Ted to read a resignation letter rather than going on television. “We have no evidence in the research to back that up, although it’s evident that it was considered,” Allen says.

Since then, the Chappaquiddick incident has been used repeatedly as a go-to insult by conservative politicians, particularly when one of their own came under the microscope of a D.C.-scandal. Faith Whittlesey, a Pennsylvania Republican and White House staff member under President Reagan, recalled thinking the incident would be “the end of Kennedy,” and that he could be blocked from the presidency for the rest of his career. The story was occasionally resurrected to point to the questions that remained unanswered, even as Kennedy remained in the Senate until his death in 2009.

Though Curran was nervous about taking on someone whose political achievements he admired (especially since there continue to be numerous conspiracy theories about the accident, including that a third person was in the car), he felt the task to be a necessary one.

“Whether you’re on the left or right side of the aisle, it’s imperative that we take a pretty hard, unvarnished look at our heroes these days,” Curran says. “The time is done to let all these guys skate by. I think if this story happened now, it would overshadow the moon landing.”

But in 1969, the reverse proved true. The closing scene of Chappaquiddick features a bit of archival footage, from a man-on-the-street style interview in Boston. A reporter asks one person after another whether they would still consider voting for Kennedy after the Chappaquiddick accident. They answer, many resoundingly, with a “yes.