Investigators have ruled that a woman found hanging naked with her wrists and ankles bound at a suburban San Diego mansion committed suicide, but the woman's sister believes otherwise.

Mary Zahau-Loehner said Thursday she found San Diego County sheriff's investigators unconvincing when they explained their findings during a visit to her home in St. Joseph, Mo.

It doesn't add up, the woman told The Associated Press. Nothing adds up.

The family wants further investigation into how Rebecca Zahau, 32, died at the oceanfront mansion owned by her boyfriend Jonah Shacknai, chairman and chief executive of Medicis Pharmaceuticals. 

San Diego County Sheriff's Department spokeswoman Jan Caldwell declined to comment about the findings, but Sheriff Bill Gore plans a news conference Friday.

Zahau-Loehner said she spoke with her sister the night before her body was found and Zahau gave no indication that she planned to take her own life. Rebecca Zahau was found dead July 13 at the mansion in suburban Coronado. Her death came two days after Shacknai's 6-year-old son from a previous marriage, Max, who was under her care, was seriously injured in a fall down the stairs. Max later died.

Zahau had been seeing Shacknai for two years.

Zahau-Loehner told The AP that investigators told her they found no suicide note, but they did share text messages on her phone from months earlier about issues between her and Shacknai's children.

Local news reports have indicated that Zahau may have grown depressed because she was reportedly watching the boy when he fell.

But Zahau-Loehner said her sister said she planned to bring Jonah Shacknai breakfast and a change of clothes the next morning to the hospital where his son was being treated, and that she would call her parents in the morning on the way to the hospital.

Too detailed planning for someone who's planning to end their life that night, Zahau-Loehner told the AP.