The Grifters
(1990)

Lilly (Angelica Huston) kills Myra (Annette Benning) in self-defense. The police mistake Myra's corpse for Lilly and label the case a suicide.

Later, Lilly accidentally kills her own son, Roy (John Cusack), while struggling with him over a suitcase full of money.

The movie ends with a distraught but determined Lilly driving off in Roy's car with Roy's blood-soaked money.

Thanks Adam!