Zahau was despondent over a sense of responsibility for the injury suffered by Shacknai's 6-year-old son Max during a time when Zahau was supposed to be watching him, authorities said. Jonah Shacknai, 54, was not home at the time.
Mary Zahau-Loehner, Rebecca's Zahau's sister, had told reporters Thursday night that the family does not believe Zahau took her own life.
Footprints on a dusty balcony and traces of DNA found on a knife, rope and bedposts helped investigators conclude that the death of a woman found hanging naked at a historic California mansion was a suicide, authorities said Friday.
The overwhelming physical evidence suggests that Rebecca Zahau bound her ankles and wrists, tied a rope around her neck and hung herself from the balcony of her pharmaceutical tycoon boyfriend's home in suburban San Diego in July, San Diego County Sheriff Bill Gore said.
The boy, Max Shacknai, had suffered injuries days earlier in a fall down the Coronado mansion's stairs. "Was Max's death a homicide? Was Rebecca's death a homicide? Other evidence included fingerprints on a knife and a message in black paint left by Zahau on the bedroom door, Gore said. No drugs were found in Zahau.
Zahau was his girlfriend of two years. No one saw Max Shacknai fall, but Zahau was home with her 13-year-old sister and heard a loud noise, investigators said.
Two days after the boy's fall, Shacknai's brother, Adam, called 911 to report that Zahau appeared to be dead, investigators said. Jonah Shacknai was not at home.
Friday's 1 1/2-hour news conference included a video reenactment of how investigators think Zahau bound her wrists.
Investigators believe Zahau cut rope that she tied to bedposts and around her wrists and ankles. Zahau's sister criticized authorities for ruling the death a suicide. Gore noted that the sister's call came before Zahau learned that Max Shacknai's condition suddenly worsened.
A portion of this shirt was reportedly originally in the decedent's mouth," Deputy Medical Examiner Jonathan Lucas wrote in the autopsy report obtained by News 8.
Zahau, 32, was found hanging from a second-story balcony on July 13 at the Ocean Blvd. home of her millionaire boyfriend, 54-year-old Jonah Shacknai.
During a 90-minute news conference Friday, San Diego Sheriff William Gore said Zahau was distraught that her boyfriend's 6-year-old son, Max Shacknai, was gravely injured in a fall down the stairs July 11. The boy died July 16, days after Zahau's hanging.
The autopsy and investigation concluded Zahau bound her own hands and feet, before looping the rope around her neck and rolling off the balcony.
Medical Examiner Investigator Dana Gary also described a message found painted on a door inside the house.
The autopsy report does not explain why Zahau may have fashioned the T-shirt to gag herself. Zahau's family said Friday they do not believe the suicide conclusion of the autopsy.
Bremner told News 8 she plans to formally request the Sheriff's Department re-open Zahau's death investigation.