Five years ago, when Mr. Jammeh first summoned Ms. Jallow to the presidential palace, she was a teenager and unaware of the scale of the accusations against the president.

“In order to know information like that, you had to be connected to the internet,’’ she said. “I didn’t even have a phone for most of my high school years. I was not very politically savvy as a teenager.”

Mr. Jammeh had told her he wanted to talk about her beauty pageant project — a drama program for students on eliminating poverty. Then he offered her a job as one of his protocol officers, who performed secretarial work at the statehouse. She was only 18, she told him, and did not feel qualified to work in a president’s office.

Later, reports emerged in the Gambian diaspora media that Mr. Jammeh had been using his “protocol girls” for sexual favors.

Advocates with Human Rights Watch and Trial International, a group that supports crime victims, took testimony from two former protocol officers who said that sex with the president had been part of the job. One woman, who did not want to be identified because she is afraid of retribution from Mr. Jammeh’s supporters, said in her testimony that when she was 23, she was given cash and gifts for having sex with him, and that he told her that if she refused he would cut off the financial support he was giving her family.

One former government official who was close to Mr. Jammeh said in an interview that several women working in the protocol office had complained to him that the president had touched them inappropriately or demanded sex. He said that in 2015 he told Mr. Jammeh to stop, and that Mr. Jammeh threatened his life and sent security officers to his house. He also said that he had seen Ms. Jallow at the statehouse at night.