I agree with Mr. Lampert. A man cannot be legally married to two women at the same time, since the second marriage is void from the outset. Actually, you could punish him a lot more by keeping him married to both, and letting both of them know of about his other marriage. They'll do a much better job of punishing him than the justice system could ever do.
If this has happened, you could also contact the local prosecutor's office and report him.