Mary Jo Kopechne had been dead for several months when her parents began to have serious questions about what had really happened the night of July 18, 1969. 

At first, Gwen and Joe Kopechne had believed Senator Ted Kennedy’s account of that evening after his car had plunged off the narrow wooden bridge on Chappaquiddick Island, just off of Martha’s Vineyard, landing upside down in a tidal pond with their daughter trapped inside. “They trusted him,” says Mary Jo’s aunt, Georgetta Potoski, 75. “They loved the Kennedys. Everyone did. But later on, they started to question what happened.”

Kennedy escaped from the car and later testified that he had tried to save Mary Jo, an idealistic 28-year-old who had worked for his brother Bobby and was in Chappaquiddick for a reunion party of her fellow campaign workers. But Ted could never escape the unanswered questions about his 10-hour delay in reporting the accident to Edgartown police.

“The longer it went on, more and more inconsistencies were discovered and he wasn’t telling Gwen and Joe anything,” says Potoski,the sister of Gwen Kopechne. “Gwen and Joe never had the last hours of their daughter’s life explained to them.”

Now, 49 years after Mary Jo’s death, a new movie Chappaquiddick, opening April 6, starring Jason Clarke as the senator, explores what happened that night and in the week that followed, when Kennedy pleaded guilty to leaving the scene of an accident.

Potoski and her son William Nelson, 46, hope the film may prompt someone to come forward with new information— and give them the answers they never got from Senator Kennedy. “The truth has never really come out,” says Nelson. “The story has never been put to rest.”

The film has not been well-received by the Kennedy camp. In an emailed statement, Kennedy legislative aide Bob Shrum writes: “As Senator Kennedy wrote in his memoir True Compass, he was at the wheel and responsible for the accident that resulted in the death of Mary Jo Kopechne, and he carried the burden of that tragic accident every day of his life.  He also understood that his pain was nothing compared to that of an innocent young woman who lost her life and her family. There have been more than 20 books and countless articles written about the accident at Chappaquiddick, some attempting to find the truth and others trafficking in conspiracy theories. This movie pretends to do the former; in reality, it does the latter, which does a disservice both to the victim and the truth.”

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In addition, literary agent Esther Newberg, who worked with Mary Jo Kopechne as one of RFK’s “Boiler Room Girls” (nicknamed for the office in which they worked) and was at the Chappaquiddick reunion that night, says, “It was frustrating to read the screenplay and see one thing made up after another, and in no way can they attest to any of it because they weren’t there and they didn’t speak to anybody who was.”

As for why she and the others who attended the party that night have rarely spoken, Newberg says bluntly: “Because it’s tasteless and in America, everyone thinks that anything is fair game for conversation and I didn’t feel that way and neither did my friends.”

Still, Potoski and her family hope that Mary Jo’s story being told on screen will result in more people learning that she was much more than just a “blonde secretary,” as she was often referred to at the time.

Potoski and Nelson have written a book, Our Mary Jo, about her life and have also launched a scholarship in her name at Potoski’s alma mater, Misericordia College (now Misericordia University), to be given out for the first time this year.

For more on the Chappaquiddick story, pick up the new issue of PEOPLE, on newsstands now.

“For 49 years people have wanted to know what happened,” says Potoski. “Maybe now, Mary Jo will be brought to the forefront and remembered not just for how she died but for who she was.”