There was "no evidence" to suggest that Ms Smith's death was the result of a crime, a police spokesman said, adding the inquiry would remain open until medical tests were complete.
Anna died only five months after the birth of her daughter, Dannielynn.
Three men are now claiming to be the father of the child, who is potentially heir to a multi-million dollar fortune.
Her partner and lawyer, Howard K Stern; ex-boyfriend Larry Birkhead; and Zsa Zsa Gabor's husband, Prince Frederick von Anhalt, say they may be the father.
Anna married Texas oil billionaire J Howard Marshall II in 1994 after being named Playboy's Playmate of the Year. She was 26 and he was 89.
He died 14 months later, Anna and Mr Marshall's family battled over his estate. The case has not yet been resolved, even though Mr Marshall's son died last year.
Anna's son Daniel died in September.
Anna said her lawyer and partner, Howard K Stern, was the father, but ex-boyfriend Larry Birkhead was demanding DNA testing before Anna died.
The husband of Zsa Zsa Gabor, Prince Frederick von Anhalt, also says he may be the father.
A judge has ordered that Ms Smith's body be preserved until a paternity hearing later this month.