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It’s been nearly 40 years since Lana Wood lost her sister – and she’s determined to find out what really happened.

In 1981, Natalie Wood’s body was found off California’s Catalina Island. The 43-year-old, who had a fear of dark water, was wearing a red down jacket and a nightgown. She had been drinking heavily aboard a yacht with her husband, Robert Wagner, and co-star Christopher Walken. The only other person aboard was the boat’s captain, Dennis Davern.

"As far as I’m concerned, we’re still on the case," Wood told Fox News. "I’m hoping that perhaps somebody’s son or daughter would have seen or remembered something. There’s got to be more people out there that know something."

The fellow actress has recently written a memoir titled "Little Sister: My Investigation into the Mysterious Death of Natalie Wood" where she sheds light on details surrounding the case and how she has fought for answers over the years.

NATALIE WOOD’S SISTER, LANA WOOD, EXPLAINS WHY SHE'S COMING FORWARD WITH KIRK DOUGLAS ASSAULT ALLEGATIONS

Lana Wood Natalie Wood

Lana Wood, a former Bond girl, is the younger sister of Natalie Wood. (Courtesy of Lana Wood)

Authorities initially ruled the death an accidental drowning. However, that changed after years of scrutiny and more witnesses emerging. In 2011, authorities reopened the investigation after Davern said he heard the couple arguing the night of Natalie’s disappearance.

The Los Angeles coroner’s office amended Wood’s death certificate in 2012 to include "drowning and other undetermined factors." The change partly because investigators couldn’t rule out that some of the bruises and marks on Wood’s body happened before she went into the water, according to the report. Wood wasn’t wearing a life jacket, had no history of suicide attempts and didn’t leave a note.

The report also revealed that investigators hadn’t preserved Wood’s fingernails to determine if she had tried to claw her way back into the dinghy. Scratch marks were found on the craft’s hull.

Then in 2018, the lead detective in the case said Wagner was considered a person of interest. The actor, now 91, has denied any involvement in Natalie’s death, and no charges have been filed. His spokesperson had no comment when Fox News reached out in regard to Lana Wood’s book.

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Robert Wagner Natalie Wood

American actor Robert Wagner and his wife Natalie Wood (1938-1981), circa 1970. (Photo by Silver Screen Collection/Getty Images)

That same year, Lana Wood and Davern participated in a podcast titled "Fatal Voyage" which pointed fingers at Wagner. At the time, a spokesperson for Wagner told Fox News: "They are despicable human beings, capitalizing on the accidental death of a beloved member of the Wagner family. They should be ashamed of themselves."

Lana Wood, who has no relationship with the actor, said she previously pleaded with Wagner to speak with the investigators handling the case.

"I couldn’t understand why he wouldn’t speak to the detectives," said the 75-year-old. "He never did. And I don’t know that he ever will. Will there ever be a deathbed confession? Probably not. It just seems to be going that way. All I can do is have the truth printed."

Lana Wood said she has zero doubts that Wagner is "responsible" for what happened to her sister.

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Natalie Wood Father

"Our dad with Natalie on the Splendour," wrote Lana Wood. "They were just sailing around for my dad’s first and last time on the boat. He died not too long after this photo was taken." (Courtesy of Lana Wood)

"There were two people on the back of the boat and then there was only one," she alleged. "I hold him accountable."

In a 2008 memoir, Wagner wrote that he and Walken argued on the night in question. When he went to bed, the star noticed that his wife and a rubber dinghy that had been tied to the yacht were missing.

"There are only two possibilities," Wagner wrote. "Either she was trying to get away from the argument, or she was trying to tie the dinghy. But the bottom line is that nobody knows exactly what happened."

Walken, now 78, has said little publicly over the years about the incident and has offered brusque replies at times when pressed. However, he told Playboy in 1997 that he thought Wood was probably half-asleep and slipped, hit her head and fell from the dinghy.

NATALIE WOOD WAS ASSAULTED BY KIRK DOUGLAS AT HOTEL MEETING, SISTER CLAIMS

Natalie Wood Dennis Davern

"Dad (who was loving being called "Fahd" by Natalie)," wrote Lana Wood. "Here he is visiting while Splendour was docked, with Dennis Davern next to him." (Courtesy of Lana Wood)

Lana Wood said it was unlikely that Natalie would have attempted to leave the boat on her own.

"That’s pretty drastic for Natalie," the former Bond girl explained. "She always had a thing about being alone. I had flown to New York a couple of times to stay with her because she would call and say, ‘There’s nobody here. How fast can you get here?’ And then I would do everything I could to get on a plane and be with her. Being alone was always an issue for her. So I can’t imagine she would try to leave a boat in the middle of the dark by herself."

Lana Wood claimed that she has tried to connect with Natalie’s daughters over the years who were raised by Wagner.

"I’ve sent countless letters and made many photo calls," she alleged. "But I understand. Their mom died and their father was the only parent they had left. So of course they were going to believe everything he said. It’s devastating what happened to those girls. But I have tried."

Robert Wagner

"In my mom’s apartment in Los Angeles, with R. J. and his mother, ‘Chat’ Wagner," wrote Lana Wood. (Courtesy of Lana Wood)

NATALIE WOOD’S DAUGHTER CALLS ROBERT WAGNER ‘COURAGEOUS’ FOR SPEAKING OUT IN DOC: ‘I WAS JUST SO PROUD OF HIM’

Lana Wood said that HBO previously approached her for its documentary "Natalie Wood: What Remains Behind." It featured interviews with Natalie’s loved ones, close friends and confidantes, including daughter Natasha Gregson Wagner. However, Wood claimed she told the network that she would agree to participate under the condition that she sat down with the 51-year-old privately.

"I wanted to make sure that she felt comfortable with me doing it," said Wood. "I didn’t get a straight answer. So I thought about it and said, ‘I can’t work with someone who thinks badly of me or doesn’t want to see me. Doesn’t want to talk to me. I’m just not comfortable with that.’ I said no. And I think that was the only time I ever turned down anything that had to do with Natalie… I guess it will always be that way."

A rep for the actress didn’t immediately respond to Fox News’ request for comment.

Lana Wood said she will continue to push for answers regarding her sister’s tragic passing. Natalie, she said, would have done the same for her.

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Natalie Wood

Natalie Wood, the three-time Academy Award nominee who starred in "West Side Story" and "Rebel Without a Cause," died in 1981 at age 43. ((Photo by Silver Screen Collection/Hulton Archive/Getty Images))

"I hope that after reading this book, people will learn what Natalie was really like and what she went through," said Wood. 

The Associated Press contributed to this report.