DENVER (CBS4) – Surveillance video from Denver International Airport should be key in the sexual assault trial of a former Marine that began Tuesday and included the alleged victim taking the stand.

Noel Bertrand, 27, is charged with sexual assault. He’s accused of attacking the woman on a concourse at DIA. He met her after they both missed flights.

READ MORE: Colorado Weather: The Mountains Will Measure Snow In Feet, Denver Will Be Lucky To Get An Inch

Prosecutors are trying to convince the jury that the woman was brutally attacked and raped in the airport, calling it a “layover turned nightmare.” But Bertrand’s attorneys argue the acts that took place at DIA that night were consensual.

Surveillance video shows Bertrand and the woman walking together in the concourse. It doesn’t show the alleged assault that is said to have occurred 30 minutes later.

Prosecutors say Bertrand aggressively forced the woman into sexual acts, but the defense says the two engaged in consensual “rough sex.” They also said she never called out for help or screamed. Prosecutors said she couldn’t talk because she couldn’t breathe due to his force and an asthma attack.

The woman had to describe the alleged rape in detail on the stand. She said while they were at the deserted gate Bertrand asked if he could kiss her and she said “no.” She said that’s when he became violent, forceful and demanding. She said Bertrand told her she was his sex slave and that he was going to teach her to feel pleasure from pain.

She told the court he pinned her head to her shoulder by grabbing her hair.

READ MORE: Staffing Issues, Mistake Lead To Cancellation Of 2 Vaccine Clinics Set Up For Coloradans To Get Boosters

“He kept his hands around the drawstrings so I was unable to breathe. I was starting to cry and I couldn’t move. He kept telling me I was going to learn pleasure from pain,” the woman said. “Every time I tried to move he kept hitting my head on the ground.”

She said Bertrand eventually got her sweatpants down and raped her. She said he slammed her head to the ground so many times to keep her subdued that she became dizzy, had blurry vision and trouble hearing.

Two airplane mechanics witnessed part of the incident through the concourse window and ran inside and eventually stopped Bertrand.

“She was on the ground. I’m pretty sure she was lying on her back, and he had her hair in one hand and was hitting her with his other hand,” witness Kris Musil told CBS4 shortly after Bertrand was arrested in 2011. Musil is a Frontier Airlines mechanic.

The mechanics told the court Bertrand told them that they didn’t know the difference between fighting and rough sex.

The officers that responded to the scene after the mechanics stopped Bertrand are also expected to take the stand in the trial.

The defense said it’s a case of misrepresentation and regret on the woman’s part.

MORE NEWS: Driver, 2 Passengers Hurt After Car Crashes Into Home In Aurora; No One In Home Injured

The woman was in DIA because she was on her way to an Illinois religious school where dating isn’t allowed.