MS-13 is an El Salvadoran street gang, known for its ruthless tactics, that has become an entrenched menace across the United States. Attorney General Jeff Sessions recently called MS-13 "one of the most dangerous criminal organizations in the US today.” Lisa Fletcher traveled to Long Island, New York, the new epicenter of rising MS-13 epidemic violence, where law enforcement officials point to flaws in current immigration policy that allow the gang to grow and thrive in America.

      Nisa Mickens was 16 years old. She loved basketball and hanging out with her best friend Kayla Cuevas. Last September, Nisa and Kayla went missing. Nisa's parents, Robert Mickens and Liz Alvarado, were desperate.

      Liz Alvarado: We were looking so hard, and we could not find her.

      After a police van drove past their house, they followed it.

      Robert Mickens: We came across another officer a few blocks away, we're looking for our daughter, and then he's like, "Do you have a picture?" I was like "Yeah, I have a picture." I showed him the picture and he looks at me, looks at Liz and goes, you know, "I'm sorry to tell you but that's your daughter."

      The students were both murdered by MS-13 members, who used machetes and bats. Since January 2016, the gang has been responsible for 21 deaths on Long Island, inspiring a visit from President Trump earlier this summer.

      President Trump: They have transformed peaceful parks and beautiful quiet neighborhoods into bloodstained killing fields. They're animals.

      Man: The purpose of the gang is take control of the town. Take control of everything that's going on with drugs, trafficking, prostitution.

      This man spent 7 years in MS-13 before he walked away, changing his appearance and his address to stay alive. He says the gang focuses on recruiting minors, especially those originally from Central America.

      Man: Back in Salvador what they do is they recruit young minors because young minors, as they get recruited and they commit a crime, they will be released, because they're minors.

      Lisa Fletcher: So how young are the kids they're targeting?

      Man: I would say thirteen, fifteen years old. The younger the better for them.

      Long Island is fertile recruiting ground because an estimated 8,000 Central Americans are here, part of a tidal wave of so-called unaccompanied minors who started pouring over the U.S. border in 2013, many of them fleeing gang violence back home. On Long Island, the minors are waiting on the courts to decide if they can stay in America or will be deported. While they wait, they are both prey and potential recruits for MS-13.

      Angel Melendez: They are very ruthless and aggressive in their recruitment tactics.

      Angel Melendez is the Special Agent in Charge for Homeland Security Investigations in New York. He is leading a new taskforce especially created to crack down on MS-13. Since June, Operation Matador has made 153 arrests, including the 6 men responsible for killing Nisa Mickens and Kayla Cuevas.

      Lisa Fletcher: Is the explosion of unaccompanied minors in the U-S leading to the rise of MS-13?

      Angel Melendez: Of the operations that we are conducting in New York, particularly in New York, the individuals that are associated with MS-13 that we've been able to arrest in the last ten weeks, are all illegal immigrants. Thirty percent of those came into the country as unaccompanied alien children.

      Melendez's team is finding some of the minors crossing the border are already affiliated with MS-13, but are being allowed to stay anyway.

      Angel Melendez: Gang affiliation is not a grounds of inadmissibility by itself. An unaccompanied alien child can present them self at the border to DHS authorities, and we would still be required to place them.

      Sen. Charles Grassley: The rise of this activity and the rise of unaccompanied children is very closely connected with the government not doing its job.

      Senator Charles Grassley chairs the Judiciary Committee that oversees the billion dollar, unaccompanied minor program. He convened a hearing last June on the topic.

      Lisa Fletcher: Is taxpayer money being well-spent on this resettlement program?

      Sen. Grassley: It's not being handled well because we find too large of a number of these kids ending up in that environment of gang activity.

      As Operation Matador continues to roll up MS-13 gang members, Liz Alvarado continues to stand watch at Brentwood High School most afternoons.

      Liz Alvarado: I'm outside at 2:30. And I watch them walk all the way home, from where I sit. I want them to be safe. I want them to go home to their parents.

      The Unaccompanied Children program will receive $1.23 billion in funding next year. Already in 2017, 38,500 unaccompanied minors have been detained at the southwestern border. In a recent speech, Attorney General Jeff Sessions claimed that some MS-13 gang members are exploiting the Unaccompanied Minors Program to enter the country as quote “Wolves in Sheep's clothing.”