WASHINGTON (REUTERS) - The FBI has added two people to its list of most-wanted fugitives: a Mexican labourer accused of killing a woman in Louisiana and a former US university professor charged with committing sex crimes in the Philippines.

The FBI is offering US$100,000 (S$125,276) for information leading to the arrests of the men, who are the 499th and 500th fugitives to be featured on the Ten Most Wanted list.

José Manuel García Guevara, 25, is a Mexican national who investigators said raped and killed a woman in Lake Charles, Louisiana, in 2008, in front of her 4-year-old stepson. Guevara and the woman lived in the same mobile home park, the FBI said.

He is believed to be in Mexico but might have travelled back to the United States, the FBI said.

Walter Lee Williams, 64, was an anthropology and gender studies professor at the University of Southern California. He left in 2011, an FBI spokesman said.

Using academic research as a guise, Williams travelled in the Philippines and elsewhere in South-east Asia to have sex with boys who were underage, according to the FBI. The bureau said it had identified 10 victims between ages 9 and 17.

"Williams allegedly utilided his position to identify at-risk youth for the purpose of sexually exploiting them and documenting those events," FBI Assistant Director Ronald Hosko said at a news conference in Washington on Monday.

Williams may have lived in Indonesia and Thailand and travelled to Mexico and Peru, the FBI said.

The Ten Most Wanted list has been in place since 1950. The bureau uses it to draw attention to some of the most dangerous US fugitives.

Of those who have been on it, 469 were caught or located, the FBI said. Others were removed when they had been on so long that publicity was no longer likely to help find them, or for other reasons.