NATALIE WOOD’s mysterious 1981 death should be reopened and thoroughly investigated, say her sister Lana Wood and case expert Marti Rulli in a bombshell new report to law enforcement officials.

“Natalie’s case is one of the most botched investigations in American history,” blasts Rulli in an exclusive interview with journalist and author Tommy Garrett.

“It’s high time for authorities to own up to it and give her the dignity she deserves.”

Oscar-nominated for “Rebel Without a Cause”, “Splendor in the Grass” and “Love With the Proper Stranger”, Natalie was 43 years old when she drowned off the coast of California’s Catalina Island on Nov. 29, 1981.

She was cruising on the luxurious 60-foot yacht Splendour with husband Robert Wagner, called RJ by pals, and actor Christopher Walken, co-star of her final film, “Brainstorm”.

Thomas Noguchi of the L.A. County Coroner’s Office ruled it an accident, theorizing the brunette beauty was awakened by the yacht’s dinghy banging against the hull and, while intoxicated, slipped and fell into the sea as she tried to secure it.

Now, Rulli and Lana want to blow the lid off the case.

“My suspicions are built on facts,” says Rulli, who penned the book “Goodbye Natalie Goodbye Splendour”.

According to Rulli, Wagner, now 81, was jealous of Walken. “Tension mounted” between them and Natalie spent the first night of the weekend cruise in a hotel with yacht captain Dennis Davern.

On that Saturday night after dinner, an angry Wagner smashed a bottle of wine in the main salon, and Walken retired to his forward cabin.

“Natalie stormed off to her rear stateroom,” Rulli tells Garrett.

“RJ followed and a terrible argument ensued that carried over to the rear outside deck. Minutes later, Natalie and the dinghy disappeared.

“My research shows RJ refused to search or to allow Dennis to turn on the searchlight or call for help. It took over two hours before RJ radioed a lame announcement that ‘someone is missing.’”

Rather than treating it as a crime scene, lawmen allowed Wagner, who claims it was an accident, and Walken, now 68, to leave in a helicopter and no one on the yacht was “checked for bruises nor interrogated,” Rulli notes.