LOS ANGELES — New witnesses have emerged in the 1981 drowning of the actress Natalie Wood, prompting investigators to deem it a “suspicious death” and name Robert Wagner, her former husband, a “person of interest,” Los Angeles County sheriff’s officials said on Thursday.

For nearly four decades, mystery and speculation have swirled around the death of Ms. Wood, who was nominated for three Academy Awards and starred in the movies “West Side Story” and “Rebel Without a Cause.”

Her death occurred on the weekend after Thanksgiving in 1981 while aboard a yacht with Mr. Wagner, the actor Christopher Walken and the boat’s captain. After a night of drinking, her body was found floating in the waters surrounding Catalina Island, off the coast of Southern California. She was 43.

Image The actor Robert Wagner in 2012. Investigators have named him a “person of interest” in Ms. Wood’s death. Credit... Frederick M. Brown/Getty Images

Investigators initially ruled it an accident but reopened the case in 2011 to see whether Mr. Wagner, now 87, or anyone else played a role after the boat’s captain said he heard the couple arguing the night of her disappearance. The coroner’s office amended Ms. Wood’s death certificate the next year to include “drowning and other undetermined factors.”

A sheriff’s department spokeswoman, Nicole Nishida, said in a statement on Thursday that new witnesses interviewed since the case was reopened gave statements that “portray a new sequence of events on the boat that night.”

One of the witnesses described hearing yelling and crashing sounds coming from the couple’s stateroom, she said. Shortly after that, separate witnesses heard a man and a woman arguing on the back of the boat and believe the voices were those of Ms. Wood and Mr. Wagner, Ms. Nishida said.

The statements differed from the original version of events provided by witnesses, including those who were on the boat, she said.

The sheriff’s department said Mr. Wagner is considered a person of interest.

“Do we have enough to make an arrest at this moment? No,” Ms. Nishida said.

The police statement was issued after CBS News aired an interview with Lt. John Corina of the Los Angeles County Sheriff’s Department, who said he did not believe that Mr. Wagner had told the whole story about what happened.

Investigators have said Mr. Wagner has not been interviewed since the investigation was reopened. They said in 2013 that they had tried at least 10 times to interview him, but that he had refused.

Mr. Wagner has denied any involvement in his wife’s death, and no charges have been filed. His publicist, Alan Nierob, declined to comment on Thursday.

Conflicting versions of what happened on the yacht have contributed to the mystery of her death. Ms. Wood, Mr. Wagner and Mr. Walken had all been drinking heavily in the hours before the actress disappeared.

Mr. Wagner wrote in a 2008 memoir that he and Mr. Walken had argued that night. He wrote that Mr. Walken went to bed and he stayed up for a while, but when he went to bed, he noticed that his wife and a dinghy that had been attached to the yacht were missing.