Oksana Grigorieva has told D.A. investigators ... Mel Gibson was so enraged the day he allegedly attacked her that he threatened that "There will be brains all over the wall" ... TMZ has learned.
Oksana went to the L.A. County District Attorney's Office Wednesday and told investigators the day of the nuclear argument, after allegedly striking her, Mel pulled out a gun, waived it around and threatened to kill her, the baby and himself, screaming, "There will be brains all over the wall."
Oksana says she fled the house with Lucia and her son Sacha.
As we previously reported -- Mel's domestic violence case is currently with the L.A. County District Attorney's Office for review.
It should be noted, claims that Mel threatened to kill himself, Oksana and the baby never came up during the mediation in May.