Paul Markham, who attended the party at Chappaquiddick the night Senator Ted Kennedy drove his car off a bridge, died on July 13.

Markham was 89.

The July 18, 1969 car accident killed 28-year-old Mary Jo Kopechne, who was trapped inside the car.

Kennedy later claimed that he, along with his cousin, Joe Gargan, and family friend Paul Markham dove in the water to try and save Kopechne that night — a claim that is still questioned to this day.

Markham, a former United States Attorney for Massachusetts, was forever linked to the many unanswered questions surrounding that night — questions that endure to this day and were explored in People’s podcast Cover Up.

On July 18, 1969, Markham attended the reunion of six men and six women (known as the Boiler Room Girls) who had been involved in the 1968 presidential campaign of Senator Robert F. Kennedy.

That night, Kennedy accidentally drove his car off the Dyke bridge. He escaped from the car, but Mary Jo Kopechne was left trapped inside. Kennedy claimed he dove in and tried to save her, but “the strong and murky current” made it impossible to get to her.

He also claimed he returned to the party cottage to retrieve Markham and Gargan for help, and that he and the two men then returned to the Dyke bridge, and repeatedly dove in the water to try and save Kopechne. But he claimed they were unable to reach her.

The three men claimed that Kennedy swam back to the hotel, and that he said he would “take care” of the accident. Markham and Gargan then returned to the party cottage where they said they waited until the next morning to tell the other guests about the accident.

It wasn’t until the next morning, 10 hours after the accident, that Kennedy went to the Edgartown police station on Martha’s Vineyard, accompanied by Markham, to report Mary Jo’s death.

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There, Kennedy dictated a statement to Markham who wrote it out in longhand and gave it to the police chief Dominick Arena. (Arena died earlier this year.) But at the time, Kennedy did not mention there had been a party the night before. Nor that there had been drinking at the party.

According to the New York Times, at the 1970 inquest, Markham said he was shocked to learn that Kennedy had not reported the accident and that a “heated conversation” between the two men ensued that morning.

Kennedy pled guilty to leaving the scene of the accident and received a two-month suspended sentence.

In an interview with the New York Times 10 years after the accident, Kennedy said he had told Markham and Gargan not to go to the police, because, he said, “I was the responsible person in the accident and I felt I should report it.”

Questions about that night dogged Kennedy for the rest of his career. And now with Paul Markham’s death, another witness to what happened in Chappaquiddick is gone.

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William Nelson, the son of Mary Jo Kopechne’s cousin, Georgetta Potoski tells PEOPLE, “It’s sad to hear of Paul Markham’s passing. I’m sure he was loved and will be missed by many. It’s a shame to see the truth about what really happened to Mary Jo slip away with each inevitable passing of those who were there that night.”

As PEOPLE reported in our podcast Cover Up, it’s not clear if the men tried to save Kopechne that night. Last year, the Kopechne family received a letter called “The Untold Story of Chappaquiddick.” The letter recounted a conversation the author had had, years later, with one of the women who had attended the party.

According to the letter, the woman said Ted Kennedy was not aware Kopechne was asleep in the back seat of the car that night. Mary Jo had laid down in the back seat of the Senator’s car when she had too much to drink and did not feel well. Then, as the letter said, Kennedy left the party with another woman in the front seat. After the car went over the bridge, they both escaped, unaware that Mary Jo was in the back seat. A discovery that was made sometime the next morning.

RELATED: 50 Years After a Woman Mysteriously Drowned in Ted Kennedy’s Car, a Letter Claims to Reveal the Truth

A second source, a friend of the Senator’s, told PEOPLE last year that Kennedy had once told him, “I did not know she [Mary Jo] was asleep in the back.”

At the time, PEOPLE reached out to a spokesperson for Kennedy’s widow, Victoria Reggie, and we were told she did not wish to comment.

Now that 50 years has passed since that night, Mary Jo’s family remains hopeful that someday the truth will still come out. “No matter what happened that night, history deserves the truth,” says her cousin William Nelson, “because as painful as it may be, there is always dignity in the truth. We hope someone will contact us in confidentiality soon, before it’s too late.”