MEXICO CITY - Mexico on Friday extradited to the United States a senior lieutenant of the Sinaloa Cartel drug gang formerly headed by Joaquin "El Chapo" Guzman, the attorney general's office said.Damaso Lopez, known as "The Graduate" because of his higher education studies, was a former security official in Sinaloa state who rose to become one of the leaders of the cartel, authorities say. He was arrested in Mexico City last year.Mexico's acting attorney general, Alberto Elias Beltran, said Lopez was seen as an important witness in the case against Guzman, who was extradited to the United States in January 2017 to face drug trafficking and conspiracy charges.Guzman's trial is expected to begin later this year.Lopez, 52, arrived in the United States on Friday and is scheduled to make an initial appearance on Monday in federal court in Alexandria, Virginia, the U.S. Justice Department said in a statement."He's a key person as much for the United States government as for the Mexican government," Beltran told a local radio program. "We can bring to a good conclusion the process the United States is carrying out against" Guzman.At the time of Lopez's arrest in May 2017, Mexican officials said he was believed to have been seeking an alliance with Guzman's rival, the Jalisco New Generation Cartel.Lopez had played a role in orchestrating Guzman's escape from prison in 2001 before joining the notorious crime group, officials have said.U.S. President Donald Trump has made security at the southern border an administration priority, arguing his plan to build a U.S.-Mexico border wall would stem the flow of drugs into the United States.He has also issued executive orders aiming to improve coordination between U.S. law enforcement and their Mexican counterparts.Mexico's next president Andres Manuel Lopez Obrador, who won by a landslide on Sunday and will take office in December, opposes the wall and has said he aims to stem drug trafficking by alleviating poverty and other root causes.Trump and Lopez Obrador discussed security issues as well as trade and immigration in a phone call on Monday, amid tensions between the neighbors over those issues.The Justice Department said later another alleged member of the Sinaloa Cartel, Arturo Lozano, made an initial court appearance in El Paso, Texas, on Friday after being extradited from Mexico on Thursday.Lozano, 47, was in charge of the cartel's warehouses in Juarez, according to an indictment cited by the department in a statement.