PHOTOS: Famous celeb breakdowns
Said Whitmore, "It's not going to be rushed."
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PHOTOS: Mel Gibson's most controversial moments
Detectives are currently investigating whether Gibson, 54, abused 40-year-old Grigorieva -- with whom he is in an ugly custody dispute over their 8 1/2-month-old daughter, Lucia -- in January.
They are examining the authenticity of the recordings, Sheriff's spokesman Steve Whitmore told the Associated Press.
He said detectives still hope to speak to Gibson, who has yet to be interviewed.
PHOTOS: Mel Gibson and Hollywood's most expensive divorces
Whitmore would not speculate on when the case would be turned over to prosecutors, who will decide whether Gibson should face criminal charges,Giorgio Armani, the AP reports.
At a closed hearing Thursday morning (attended by several sheriff's investigators), detectives received profanity-laced recordings in which Gibson apparently launches a verbal attack against Grigorieva.
Mel Gibson's soon-to-be ex-wife Robyn has filed a written, sworn declaration to the courts defending him in his possible domestic violence case, according to TMZ.
In her 1-page declaration, she states: "Mel never engaged in any physical abuse of any kind toward me before, during or after our marriage," the website states.
During their 28 years of marriage (she filed for divorce last year), "Mel was a wonderful and loving father" to their seven children, she declares, according to TMZ.