Dennis Davern, one of the last people to see Natalie Wood alive, has written an open letter to police saying Robert Wagner "deserves to be arrested" for his late wife's death, RadarOnline.com has exclusively learned.
Davern, skipper of the couple's yacht, also told Radar he passed a police-administered polygraph testing fingering Wagner as the cold-blooded killer!
Among the damning statements in the April 12 letter, obtained by Radar, is this chilling passage: "I know what RJ (Wagner's nickname) did to Natalie. There's plenty of evidence, but the higher-ups are stalling in seeking justice for a woman who deserves it."
For the first time, Davern has also revealed details of the explosive polygraph, which prompted police to reopen the homicide investigation into the West Side Story star's death.
"When detectives had me hooked up to their polygraph test equipment, I was asked, 'Did Robert Wagner murder Natalie Wood?'"
Dennis said, "I answered, 'Yes' — and I passed!"
He decided to speak out after Wood's eldest daughter, 45-year-old Natasha Gregson Wagner, implied people who think Wagner murdered the actress are "conspiracy theorists."
Dennis was one of only four people aboard the Splendour on the night of Nov. 29, 1981 and wants Gregson Wagner to realize her beloved 86-year-old stepfather isn't as innocent as he claims.
"I always wonder if (Natalie's) girls know I passed the polygraph – that I'm not just saying these things!" Davern said.
Gregson Wagner, whose father is film producer Richard Gregson, discussed her mother's death while promoting her fragrance, Natalie.
Gregson Wagner, 11 when her mother died, has said the facts behind the fatal plunge "don't concern me," and blasted allegations against Wagner as "preposterous."
"It's perplexing why details would not matter to a daughter," Marti Rulli, co-author of Goodbye Natalie, Goodbye Splendour told Radar.
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Many close to the late actress are furious Gregson Wagner is cashing on her dead mother's name while defending the actor, who police still call "a person of interest" in the case.
"It's disgusting that Natasha evokes her mom's memory, but protects Robert Wagner despite all the evidence against him," an insider told Radar.
Dennis has directly implicated Wagner in Wood's death, saying the actor flew into a violent rage aboard the Splendour, accusing Wood of having an affair with her Brainstorm co-star Christopher Walken, also on board that night.
"The last expression I saw on her face was pure humiliation as she stormed off to her stateroom," Davern revealed to Radar.
Her death was ruled an "accidental drowning," but the case was reopened in 2011. The cause of death was changed to "drowning and other undetermined factors" due to bruises on her body.
In his letter to authorities, Davern wrote that when Wood's lifeless body was discovered in the water, "I saw the bruises."
But Wagner convinced him to stay quiet "to spare Natalie's daughter," he said.
Now, Davern told Radar: "That was the worst mistake I ever made! As a witness to that horrible night, I believe Natalie was murdered.
"The detectives never questioned my credibility. It's only been questioned by the fans that the Wagner family continue to dupe!"
Find out more of the shocking secrets and scandals surrounding Natalie Wood's death, on this week's episode of National Enquirer Investigates, Saturday night at 9 pm PT/ET on REELZ Channel.