People who immigrated to the United States illegally are responsible for an increase in gang violence in Frederick County, Maryland, the county’s sheriff said Tuesday at a congressional hearing on immigration reform.

Sheriff Charles Jenkins said before the House Subcommittee on Immigration and Border Security that immigrants in the U.S. illegally are committing crimes in the county and recruiting in local schools.

“Some of the problems that have started in the communities with the gang presence is now spreading into our high schools — some of it into our middle schools. [At] one of the local high schools, routinely [there are] fights between rival gangs,” he said, referring to Frederick High School.

Jenkins said more than 75 gang members are active in Frederick County. The sheriff said he believes the 18th Street Gang and MS-13 are recruiting in schools.