MEXICO CITY — Yazmín Morales recalls weeping with rage after an encounter four years ago in the book-lined study of her country’s most respected statesman. Óscar Arias Sánchez, a Nobel Peace Prize laureate and former Costa Rican president, had pinned her against a door, she says, forcibly kissing and groping her.

Until last week, Ms. Morales kept the episode to herself. But after another woman came forward to file a criminal complaint against the former president alleging sexual assault, Ms. Morales summoned the courage to add her voice.

Ms. Morales, a former Miss Costa Rica, wanted a powerful criminal lawyer to represent her. She called one, then another. After a third also refused to take her case, she decided to act alone. Accompanied only by her half sister, she, too, filed a criminal complaint against Mr. Arias.

The case of Mr. Arias, who now faces accusations of sexual assault or misconduct from at least nine women, is emerging as the most significant of the #MeToo era in Latin America.