As one law enforcement source said ... the second round of questions shows how seriously the Department is taking the investigation of Oksana Grigorieva and Mel's claim that she tried extorting him for millions in connection with the incendiary tapes.
We're told Mel has cooperated with investigators and will continue to cooperate by sitting for another interview. Our law enforcement sources say ... investigators informed Mel's lawyer they won't ask questions about the domestic violence case.
As we first reported ... the Sheriff's Department turned the domestic violence case over to the D.A. Wednesday but the extortion investigation continues.