The decision was announced Friday, soon after prosecutors filed a misdemeanor battery charge against the Academy Award winner.
Attorneys for Oksana Grigorieva say she cooperated fully with the investigation into extortion allegations by Gibson.
Attorneys Daniel Horowitz, Ronald Litz and Martin Garbus said in a statement released to The Associated Press that the Russian musician never invoked her Fifth Amendment rights during several interviews with authorities.
Gibson claimed Grigorieva attempted to extort him during custody negotiations involving their infant daughter after their breakup last year.
The attorneys said they would not release any further statements.
