A Spirit Airlines plane. (Bill Montgomery/Houston Chronicle/AP)

It was a late-night flight from Las Vegas, and the woman rested her head on the window as the plane neared Detroit.

She was startled awake by the man in the middle seat next to her. His hand was down her unbuttoned pants, and her shirt was undone.

The 22-year-old woman fled to the back of the plane to alert flight attendants.

But first she had to get past two obstacles: Prabhu Ramamoorthy, the man in the middle seat, and his wife in the aisle seat — an arm’s length away from a chill-inducing Jan. 3 incident later described in court.

A federal jury convicted Ramamoorthy, 35, of sexual abuse on the Spirit Airlines flight. Ramamoorthy, an Indian national in the United States on a work visa, faces up to life in prison. He will be deported after serving his sentence, U.S. Attorney Matthew Schneider said in a statement.

“Everyone has the right to be secure and safe when they travel on airplanes. We will not tolerate the behavior of anyone who takes advantage of victims who are in a vulnerable position, and we are glad the jury agreed,” Schneider said. “We appreciate the victim in this case for her courage to speak out.”

Jurors deliberated 3½ hours before returning their decision, he said.

Ramamoorthy initially told investigators he had taken a pill and fallen into a deep sleep. He said he hadn’t done anything besides learning from his wife that the woman, who was not named in the complaint, was sleeping on his knees.

He and his wife later acknowledged the pill was plain Tylenol, according to prosecutors, and gave conflicting reports of what happened. His wife told investigators that she asked to switch seats because of the woman falling asleep, but the attendants told authorities no one else had asked to switch seats other than the victim. The wife was not named.

Ramamoorthy told an FBI agent he “might have” unhooked the woman’s bra and then unzipped her pants, the complaint said. He tried to put his fingers inside the woman, he said, but he told the investigator he was unsuccessful.

But the prosecution presented evidence Ramamoorthy penetrated the woman with his fingers, Schneider said.

Ramamoorthy could not be reached for comment. His attorney James Amberg and Spirit Airlines did not return a request for comment.

In the trial, Amberg said his client’s understanding of the legal process was based on Indian law. Ramamoorthy believed anything he told police was inadmissible in court, according to a motion Amberg filed to suppress Ramamoorthy’s statements.

He also believed he would be tortured unless he gave incriminating statements, the motion said. Amberg cited “Visaranai,” a 2015 Indian film about corrupt police using violence to coerce guilty pleas, as evidence of Ramamoorthy’s belief he faced a similar threat in the United States.

It is not clear if Ramamoorthy will appeal the conviction.

The FBI, which investigates crimes on aircraft, has said sexual assault in the air has increased in recent years. There were 63 reports of sexual assault on flights last year, the agency said, up from 38 in 2014.

David Rodski, an FBI special agent assigned to investigate crimes out of Baltimore-Washington International Marshall Airport, said many incidents either go unreported or victims take time to alert authorities, The Washington Post’s Lynh Bui reported in June.

“Hit that call button . . . notify the flight crew immediately,” Rodski said.

Eli Rosenberg contributed to this report.

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