But the report, written in June 2012, said there was not enough evidence to say that her death was definitively "non accidental."
The body of the "West Side Story" star, 43, was found floating in a Santa Catalina Island cove off the coast of Southern California in 1981 after she had spent a night of dining and drinking on the island and on a yacht with her husband, television star Robert Wagner, and actor Christopher Walken.
The case has been surrounded by mystery and suspicion for decades and Los Angeles homicide detectives reopened the investigation into Wood's death in 2011.
In June 2012, authorities changed Wood's death certificate to "drowning and other undetermined factors" from the original finding of accidental drowning, but did not explain why.
The change was based on a 10-page document, drawn up as an addendum to the original autopsy report, that said Wood died shortly after she entered the water.
"The location of the bruises, the multiplicity of the bruises, lack of head trauma, or facial bruising, support bruising having occurred prior to the entry into the water," the supplemental coroner's report states.
"This medical examiner is unable to exclude non-volitional, unplanned entry into the water ... Since there are many unanswered questions and limited additional evidence available for evaluation, it is opined by this medical examiner that the manner of death should be left as undetermined," it adds.
A spokesman for the Los Angeles County Sheriff's Department said on Monday the case was still open but declined to discuss any new evidence that may have been discovered.
The Sheriff's Department has said that neither Wagner, now 82, nor Walken are suspects.
Wood starred opposite James Dean in the classic 1955 film "Rebel Without a Cause," and later in musical "West Side Story" and "Splendor in the Grass."
(Reporting by Eric Kelsey; Editing by Mohammad Zargham)