( CNN ) -- Mexican authorities have arrested a former college professor who was on the FBI 's 10 most wanted list over allegations of child sex abuse . Walter Lee Williams was detained late Tuesday , Mexican state news agency Notimex reported . The FBI placed the former university professor wanted for alleged sexual exploitation of children on the list Monday , according to Notimex . Williams researched in the field of gender development at a university in California , which gave him easy access to his victims , mainly teenage boys in developing countries , the FBI said . Agents believe he had resided in Indonesia , Polynesia and Thailand , but also may have traveled to Mexico and Peru . An FBI agent reported finding child pornography on a computer and in a video camera belonging to Williams . He was the 500th suspect added to the `` FBI 10 most wanted fugitives '' list , and the bureau offered $ 100,000 for information leading to his arrest . Williams ' photo had appeared in Mexican newspapers identifying him as a fugitive . Police arrested him in a cafe in Playa del Carmen after he failed to produce proper identification .
Walter Lee Williams was a professor studying gender development . He had been researching the effects of hormones on children and adolescents for years, but he didn't think much about it until his wife died in childbirth with their first child. The FBI offered $ 100,000 for information leading to his arrest . It believes Williams lived in Indonesia and Thailand and traveled to Peru and Mexico .