I think that many of us have been critical of the US government's over-hyping of international links between MS-13 and 18th Street gangs and the extent to which they have been carrying out violent attacks in the US. It's not that there are no links or that no gangs are active. It's more that the fear-mongering seemed to be more politically motivated than based on much empirical evidence.
Michael E. Miller and Dan Morse Local take a look at how the has been a resurgence of MS-13 gang activity in Maryland in ‘People here live in fear’: MS-13 menaces a community seven miles from the White House for the Washington Post. The stories are similar to what I have heard from friends and family in New York.
As in Long Island, the MS-13 is preying on the most vulnerable. They are trying to recruit some of the undocumented minors who have fled to the US in recent years. These youth are often separated from family members, have difficulty speaking the language, and look for fraternity in a US political environment that treats them with suspicion and rejection. If soft recruitment doesn't work, threats and violence will.
The MS-13 is also preying upon undocumented migrants from Central America. The migrants are reluctant to involve police because of their immigration status. The migrants are also scared to pursue charges against the MS-13 members because even if US authorities were able to successfully charge and prosecute gang members in the US, the gangs have threatened victims' family members in El Salvador, Guatemala, and elsewhere in Central America. There's little that the US or Central American authorities can or will do about that.
There's no single solution to the violence. However, legalizing the status of undocumented migrants would help, as would improving the trust between police and people who live in these communities, particularly undocumented migrants. Instead, the Trump administration's policies are making matters worse.