Sources tell TMZ ... the Sheriff's Department investigation into Oksana Grigorieva's complaints against Mel Gibson involve three possible offenses -- domestic violence, child endangerment and assault with a deadly weapon ... and the case will go to prosecutors this month.
Sources tell TMZ the Sheriff's Department investigation will last approximately 2 more weeks.
And sources say Mel's lawyer has made arrangements to make "a presentation" to Sheriff's investigators and that Mel "might be made available at a future date."
We're told the case will be referred to the L.A. County D.A.'s Office for felony review.