The suit was filed Friday in federal court by the family of 32-year-old Rebecca Zahau and seeks general and punitive damages. Zahau was found hanged at a Coronado mansion in July 2011. Her death was ruled a suicide.
But Zahau's family always believed her death was suspicious. The lawsuit claims Adam Shacknai and Dina Shacknai, the brother and ex-wife of Zahua's boyfriend, Jonah Shacknai, and Dina Shacknai's twin sister, Nina Romano, were responsible for the woman's death. The filing of the lawsuit was first reported by U-T San Diego.
The lawsuit doesn't provide any specific evidence against the three, but alleges "defendants planned and prepared to batter and murder Rebecca and did thereafter brutally, and with malice aforethought, stalk, attack, choke, bound and hang" Zahau at the mansion belonging to her billionaire boyfriend. Jonah Shacknai was not named in the lawsuit.
No criminal charges were filed.
Attempts to reach Adam Shacknai, Dina Shacknai and Nina Romano on Sunday were unsuccessful.
Authorities said Zahau killed herself because she was distraught over a fatal fall that Shacknai's 6-year-old son suffered at the house two days earlier. His death was ruled accidental.
Adam Shacknai was staying in a guesthouse at his brother's historic Spreckels mansion at the time of Zahau's death, the U-T reported. Dina Shacknai was staying in a separate vacation home a few blocks away, and Nina Romano had flown in from Sacramento to be with her sister.
Adam Shacknai told police he found Zahau hanging by a rope from a second-story balcony at the mansion, and cut her down. Her hands were bound behind her back, her feet were bound and a T-shirt was wrapped around her lower face.
The remodeled mansion was sold last month for $9 million to the owner of a private aircraft company in Utah.