A Los Angeles County District Attorney has been presented with evidence about the case - relating to the guarantee she would not release the tapes which see Mel threaten her as part of a child custody agreement for their two-year-old daughter Lucia - and will now decide if the Russian-born singer will face official charges.
District Attorney spokesperson Jane Robinson told E! News: "Sheriff's officials dropped off last part of the Mel investigation today. It's under review."
Being questioned is whether Oksana intentionally tried to gain $15 million in hush money to prevent the recordings from going public.
Soon after signing the child custody agreement, Oksana reneged and the recordings appeared a few months later, although she has always denied her involvement.
Discussing the taped phone call - which sees the 'Braveheart' actor call her a "****" and a "f***ing selfish b***h" - last year, the 40-year-old star said she began recording when she was scared she would not make it "through the night".
She said: "I started taping it around 11 o'clock because I thought I'm actually not going to live through the night. I wanted my mother to be able to prove that if I'm dead that this is who did it. "