Trial begins for woman accused of killing twin sister by driving off Hawaii cliff Alexandria Duval is accused of killing her twin, Anastasia Duval, in 2016.

 -- A murder trial is underway for a woman accused of purposefully driving off a cliff in Hawaii, killing her identical twin sister.

On May 29, 2016, Alexandria Duval was driving along the winding Hana Highway in Maui with her twin, Anastasia Duval, in the passenger seat when the car plunged off a cliff.

Alexandria Duval survived the 200-foot fall, but her twin died at the scene.

The sisters, born Alison and Ann Dadow, ran popular yoga studios in Florida before changing their names, according to The Associated Press. They moved to Hawaii in 2015.

Alexandria Duval, 39, is charged with second-degree murder and has pleaded not guilty.

Maui deputy prosecuting attorney Emlyn Higa said in his opening statement today that Alexandria Duval "intentionally or knowingly" drove off the cliff.

Defense attorney Birney Bervar, however, called the deadly car crash a "tragic accident, not murder."

About an hour before the crash, another driver, Randolph Castro, saw the Duvals' SUV swerving and saw other cars get out of their way, Higa said. Castro followed them and allegedly saw the Duvals stop a few times, the prosecution said.

At one point Castro allegedly saw the two sisters "physically fighting within the car," and when Castro tried to find out what was going on, "the defendant just drove off again," Higa said.

Another witness allegedly heard "screaming coming from within the SUV" and claimed to hear the driver yell approximately three times about needing a psychiatrist, Higa said.

Alexandria Duval allegedly later stopped the SUV with the hazard lights on and continued to physically fight with her sister, the prosecution said.

After that, a witness allegedly said he heard the roar of the SUV's engine and watched the SUV accelerate down the road, driving straight until it "suddenly jerked" to the left and went over the cliff, Higa said.

Higa said the case comes down to three facts: He alleges there was a hard acceleration, a hard left turn and no braking. Higa said the prosecution will present evidence from the road, the eyewitness who saw the crash and the data retrieved from the SUV that he said "indicated that the brakes were not used and quantifies the acceleration and the turn."

Defense attorney Bervar in his opening statement said that he will show evidence from witnesses, the road, the car and the victim's body to prove the crash was not criminal but a "tragic accident."

Bervar said Anastasia Duval was "violently" pulling Alexandria Duval's hair in the car.

"Several eyewitnesses ... witnessed violent fighting and hair pulling -- that the passenger was violently pulling my client's hair with both of her hands -- pulling it so hard it was jerking her head over the passenger side seat," Bervar said.

The hair pulling was so violent, Bervar said, that found in the victim's hands were long blonde hairs from Alexandria Duval.

Bervar said photos of tire marks will "show the car not taking a sudden left turn, but just running off the road."

Witness Chad Smith testified that he saw the two women in the car on the road and that it appeared they were "arguing" with their hands up, angry, and yelling at each other.

A police officer also took the stand to testify that the car involved sustained heavy damage and that when he pulled over, the passenger was foaming at the mouth and seemed to have "major head trauma."

Alexandria Duval agreed to waive her right to a jury trial and her fate will be determined by the judge.

ABC News' Lisa Sivertsen, Julia Jacobo and Morgan Winsor contributed to this report.