TMZ said the coroner has issued a new death certificate to that effect.
At the time, in 1981, it was determined that Wood drowned accidentally after drinking on a yacht off Catalina Island with her husband, Robert Wagner, and actor Christopher Walken. The investigation was reopened last November.
According to TMZ, detectives now believe that some of the evidence is inconsistent with drowning, and they can't prove whether it was an accident or foul play.
A statement from Capt. Mike Parker, a sheriff's department spokesman, simply says, "It remains an open and ongoing investigation. There are no further details."