Reputed Los Angeles gang member Joe Luis Saenz was taken into custody in Guadalajara late Thursday following a joint operation with the Mexican government, said Bill Lewis, assistant director in charge of the FBI's Los Angeles office.
Investigators said Saenz shot and killed two rival gang members in July 1998 to retaliate for an assault on one of his associates.
Saenz suspected Sigrieta Hernandez, his girlfriend and the mother of his daughter, was going to tell police about the slayings, investigators said. He is accused of kidnapping, raping and killing her less than two weeks later.
Saenz also is believed to have killed Oscar Torres at his home in suburban Whittier in October 2008 because he failed to repay $600,000 in drug money after police seized the cash during a traffic stop. Authorities said they have videotape from a surveillance camera at Torres' house that shows Saenz killing Torres and wounding another person.
Saenz, who is about 37 years old, was believed to be hiding in Mexico, working as an enforcer and hit man for a Mexican drug cartel.
Saenz had been on the FBI's most-wanted list since 2009, putting him among the ranks of Osama bin Laden, Boston crime lord James "Whitey" Bulger and other notorious criminals. There was a reward of up to $100,000 for information leading to his arrest.