Mexican President Andres Manuel Lopez Obrador on Wednesday urged the United States to reveal the whereabouts of a notorious drug trafficker whose name has disappeared from the U.S. prison register.Edgar Valdez Villarreal, a Mexican-American nicknamed "La Barbie" for his fair complexion, was captured by Mexico in 2010 and extradited to the United States, where he was sentenced to 49 years in prison.The Bureau of Prisons told AFP that the Texas-born Valdez "is not currently in the custody" of the U.S. federal agency, which could be for several reasons.According to prosecutors, Valdez began his drug trafficking career in Laredo, Texas, and soon developed cocaine customers in New Orleans and Memphis.When Valdez was sentenced in 2018, the Justice Department said he was "ruthlessly working his way up the ranks of one of Mexico's most powerful cartels, leaving in his wake countless lives destroyed by drugs and violence.""