HOMICIDE detectives should arrest Hollywood star Robert Wagner and question him over the death of his late wife, Natalie Wood, her sister told The National ENQUIRER in a world exclusive interview.

On the eve of the 33rd anniversary of Natalie’s mysterious death, a furious Lana Wood declared: “R.J. should be arrested and taken in for questioning like any regular Joe!

“Because he’s Hollywood royalty, they’ve treated him with kid gloves. I want to know what really happened to Natalie so this case can be closed and she can rest in peace.”

Lana, 68, added: “If they find proof that he (Robert) was directly involved in her death, then he should be charged.”

Natalie, star of “West Side Story,” was 43 when she died Nov. 29, 1981. She and Wagner, now 84, had been entertaining her “Brainstorm” co-star Christopher Walken aboard their yacht, “Splendour,” off California’s Catalina Island.

While Wagner has admitted arguing with Christopher that night, he claimed Natalie left them and went to the yacht’s master cabin. Her body was later found in the water.

Now, in a stunning declaration, her still-grieving sister has penned a heartbreaking “open letter” to Wagner, which was obtained exclusively by The ENQUIRER.

Authorities have not yet labeled Wagner a suspect, and his lawyer, Blair Berk, has said the former “Hart to Hart” star “fully cooperated” with police.

But Lt. John Corina of the Los Angeles County Sheriff’s homicide division told The ENQUIRER that Wagner has dodged investigators’ questions for nearly three years.

If he “is innocent, then he has nothing to fear” from talking to detectives about that night, Lana told The ENQUIRER.

FOR THE FULL STORY and to read Lana’s heart-rending letter it’s ONLY in the new ENQUIRER – on sale NOW!