A woman's car plunged off a cliff, killing her twin sister. Now police think it was murder.

It looked like a horrible, tragic accident. A woman killed when her twin sister lost control of her car, sending it plunging over the edge of a rocky cliff.

But now police believe it was a much more sinister story.

The driver, Alexandria Duval – who also goes by the name Alison Dowdal – has been charged with second degree murder over the death of her identical twin Anastasia Duval, after witness accounts revealed that the 37-year-old women appeared to be having a heated argument right before the crash.

The Duval twins. via WPBF

The women were driving along Hana Highway on the Hawaiian island of Maui when Alexandria's Ford Explorer SUV accelerated forward and took a sharp left before driving over the edge of a cliff and landing on the jagged rocks below.

Alexandria was airlifted to hospital in a critical condition, but her sister was pronounced dead at the scene.

One witness to the accident told local station KHON2 that he saw the passenger pull the driver's hair, before the car suddenly took off and sped toward the cliff edge.

"My first thought when she was coming past was 'Don't hit me, don't hit me'," the witness said, "Because she was slightly out of control."

Court documents show that investigators examining the car's airbag control module found no evidence that Alexandria attempted to brake prior to reaching the cliff's edge.

Alexandria's lawyer, Todd Eddins, has maintained the crash was an accident, calling the event a "heart-shattering tragedy" for the Duval family.

“Alison did not try to harm herself or the person she most loved and was closest to in the world,” said Eddins.

Alexandria is currently being held without bail and is due to face a preliminary hearing today.