MS-13 graffiti marks a highway bridge in Springfield, Va.,near where police found the body of 15-year-old Damaris Alexandra Reyes Rivas on Feb. 11. (Michael Miller/TWP)

With gang recruitment increasing inside Fairfax County Public Schools, assaults and other types of violent crimes have also been on the rise in every police district in the county, police officials told the County Board of Supervisors on Tuesday.

Regionally, incidents of illegal sales of guns and drugs in addition to sex trafficking have also increased.

“Unfortunately, we see ourselves as reactive” to the problem, Police Chief Edwin C. Roessler Jr. said at a public safety committee meeting that focused on a resurgence of violent activity by the transnational Mara Salvatrucha gang, better known as MS-13.

Fairfax police said teenagers from the county have been involved in several of the seven gang-related killings that have occurred in Northern Virginia in recent months.

Detectives are still investigating whether two bodies found early this month in Holmes Run Park are linked to gang activity. They have already concluded that the Central American gang was behind the death of a 15-year-old Maryland girl found at a Springfield industrial park.

Supervisor Penelope A. Gross (D-Mason), whose district includes the Holmes Run Park site where the two bodies were recently found, argued Tuesday for more urgency in county efforts to expand social-service programs geared toward at-risk youths.

She characterized as “lackadaisical” gang-prevention efforts put into place after a surge in gang violence in the wealthy county during the late 1990s.

“We should be angry about this,” Gross said, her voice rising. “In the whole community.”

Figuring out which youths are involved in gangs is getting to be a tougher chore, Jay Lanham, director of the Northern Virginia Regional Gang Task Force, told the supervisors.

Few teenagers affiliated with MS-13 wear identifying colors or hang out in the same spots the way previous generations of gangs did, Lanham said. Most of them communicate with one another on social-media websites, where the bulk of the recruiting occurs.

“They are advertising on social media; they are posting on Facebook regularly,” Lanham said. “They’re using a lot of these social apps to do this, and it’s very difficult to follow, and it’s difficult to stop it.”

The hearing exposed a current of resentment over changing demographics in the county of 1.1 million residents, which in recent years has become more Latino and Asian.

Supervisor Pat Herrity (R-Springfield) blamed the gang problem on the arrival in Fairfax County Public Schools of unaccompanied minors from Central America, many of whom came to the United States illegally after fleeing violence in El Salvador, Guatemala or elsewhere.

Under federal law, the school system is required to accept such students.

“We’ve had about 1,500 undocumented minor children in our school system over the last couple of years, so this problem really shouldn’t be too surprising,” Herrity said. “A lot of these children can’t read or write in their own language. It puts a huge burden on our school system. It puts a huge burden on our police department and our communities.”

Other supervisors said they want to be careful not to tap into fears over ramped-up federal immigration enforcement efforts, which advocates and police say can inhibit cooperation with police on gang-related crimes.

“We know we have a lot of native-born kids who are being recruited into gangs,” said Supervisor John C. Cook (R-Braddock).

“We don’t want to be overreacting to something we see in the newspapers. But we certainly want to make sure that when it comes to kids in our schools that we’re giving them good alternatives so that we’re counteracting the bad influences.”