Walter Lee Williams, former USC professor, is 500th person to be added to FBI's "Ten Most Wanted" list

Walter Lee Williams is the 500th person to the FBI's Ten Most Wanted list on Monday.

(CBS/AP) WASHINGTON-- Walter Lee Williams, a former University of Southern California professor, became the 500th person named to the FBI's Ten Most Wanted fugitives list Monday.

PICTURES:  FBI's Top Ten Most Wanted Fugitives

Of the 500 fugitives who have been named to the list, 469 have been apprehended or located, according to the FBI. Of those, 155 fugitives were located with the help pf the public.

Williams is wanted for allegedly sexually exploiting children and traveling abroad to engage in sex acts with minors.

Williams has traveled to the Philippines and is believed to have lived in Indonesia, Polynesia and Thailand.

Also named to the list Monday was the 499th person, Jose Manuel Garcia Guevara, accused of murdering 26-year-old Wanda Barton in front of her 4-year-old stepson in Lake Charles, La. in 2008. The FBI believes that Guevara raped Barton before stabbing her to death.

The FBI believes Guevara is currently in Mexico but said that there is a possibility that he returned to the US using falsified documents.

Guevara was indicted by a grand jury in April 2008 on charges of second-degree murder, aggravated rape and aggravated burglary.