Officials have ruled the death of Rebecca Zahau, the girlfriend of San Diego billionaire Jonah Shacknai, as a suicide, but family members say they believe she was murdered and they have an inkling who did it.

Zahau's naked body was found hanging from a balcony on July 13 at Shacknai's historic Spreckels Mansion in Coronado. The home boasts 27 rooms. Shacknai is chairman and chief executive of Medicis Pharmaceuticals. She had been seeing Shacknai for two years.

Zahua's death came just two days after Shacknai's 6-year-old son, Max, who was under her care,was seriously injured in a fall down the stairs. Max later died as a result of the incident.

Zahua's sister Mary Zahau-Loehner, on Thursday said she found the findings of San Diego County sheriff's investigators unconvincing during a visit to her home in St. Joseph, Mo. The family wants further investigation into how Zahau, 32, died.

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

San Diego County Sheriff's Department spokeswoman Jan Caldwell declined to comment. Sheriff Bill Gore plans a news conference on Friday.

Zahau-Loehner said she isn't convinced because she spoke with her sister the night before her body was found and there was no indication that Zahua planned to take her own life.

Zahau-Loehner also said investigators told her they found no suicide note. They did however, share text messages on her phone from months earlier about issues between her and Shacknai's children.

There have been reports from local media that Zahau may have grown depressed because she was reportedly watching the boy when he fell.

Becky did not kill herself, someone killed her, Snowem Horwath, Zahau's sister, told RadarOnline.com. Time will reveal who killed Becky. I think I know who killed my sister. We are not stupid; she never had any enemies.

Horwath didn't say who she believes killed her sister, but disputed the evidence the police told her family they used to rule the death as suicide.

They do not have enough evidence to say it is a suicide, it is such a big lie, Horwath told RadarOnline.com, noting also that the family felt that there were many holes in their theories. Things they said did not match and they said they had a text message on her phone that showed that she was very unhappy, but they didn't even say if it was from her or from someone else, or if someone could have put it there.