Criminal networks with Latin American roots, such as MS-13 and the 18th Street gang, are using the administration’s open-door policy at the border to slip in recruits that are causing a huge spike in murder and violence throughout the nation, according to an immigration expert. Testifying Thursday at a House hearing on the border surge of young Latinos, the expert said, Established gangs have been able to transfer an unknown number of experienced foot soldiers from Central America to help colonize new criminal territory in the United States. Jessica M. Vaughan, the policy director for the Center for Immigration Studies, told the House Judiciary Committee’s Immigration and Border Security subcommittee that the tide of new young people, many of whom have already been exposed or involved in street gangs at home, has provided a huge pool of new recruits for the gangs here. Gangs such as MS-13 and 18th Street are enjoying a brutal revival in certain parts of the country and are establishing themselves in new places. Jessica M. Vaughan discussing the issues of visa overstayers.