Long Island, New York (CNN) The first time members of the MS-13 street gang attacked Margarita's teenage son in suburban New York, they beat him with a baseball bat.

The young man had immigrated from El Salvador three months earlier to join his mother in Nassau County, Long Island. The gang had harassed him in El Salvador because he refused to join them. Now, in his new home, they were upping the stakes.

The second time, they attacked the 19-year-old as he was on his way to work. They slashed him in the stomach with a machete, the gang's weapon of choice. He survived and has been in hiding for the last few weeks, but his mother is terrified.

"I think it's worse (in the US) because over there they hadn't tried to kill him. But here they have," said the woman, who is undocumented and asked to be called only "Margarita" for her safety. She witnessed the first attack on her son, on the street outside their home, and says she's too afraid to go to the police for fear of deportation.

The violent gang known as Mara Salvatrucha, or MS-13, originated decades ago among Salvadoran immigrants in Los Angeles and has since built a criminal network that extends across the US, with thriving pockets in the Washington, D.C. suburbs and here on Long Island, just an hour or so east of New York City. It's estimated to have 10,000 members nationwide.

President Trump has vowed to wipe them out and will visit Long Island Friday to discuss his plans. But the FBI says the gang is growing.

Investigators comb woods where the mutilated bodies of four young men were discovered in late April in Central Islip. Authorities believe MS-13 was behind the killings.

And several people familiar with MS-13, including two gang members themselves, told CNN they think Trump's crackdown on immigrants is actually making MS-13 stronger because witnesses are more reluctant to come forward for fear of being deported.

"It's not like before, where ... they (the gang) were more hidden," said Margarita, adding that a decade after fleeing violence in El Salvador she has never felt more afraid. "People can get deported, so they don't call the police. So they (MS-13) feel more free."

"I think it's emboldening them, because this gives them the opportunity to tell immigrants, 'What are you gonna do? Are you going to report us? They're deporting other innocent people ... (so) they're going to associate you with us by you coming forward,'" said Walter Barrientos, Long Island coordinator with Make the Road , an immigrant advocacy group.

"'So what are you going to do? Who's going to protect you?' And that's what really strikes many of us."

But a senior Trump administration official disputed that thinking.

"The reality is that we are removing MS-13 and other criminal gang members in very large numbers, and they are hurting," the official said.

"As far as reporting crime is concerned, the biggest impediment as I said earlier, is sanctuary cities, where ... illegal immigrant gang members are released from a prison or jail and then we have to go searching for them at great costs ... and at great personal risk to the officers.

"If you want to be looking at strategies that need to change and change right away, sanctuary cities would be at the top of that list."

'We're targeting you'

While MS-13 has had a presence in the U.S. for decades, the level of violence and activity has risen considerably in the last two years, according to the FBI. And in recent months here, authorities say the gang has been on a killing spree.

In the last two years, the FBI says MS-13 has committed more than 20 slayings on Long Island, drawing national attention to the gang's growing presence.

Last September, two teenage girls from Brentwood were beaten to death in a case that put Nassau and Suffolk counties on the map as an epicenter of MS-13 activity.

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In April, the bodies of four young men, ages 16 to 20, were discovered in a park in Central Islip. They were beaten with wooden clubs and their bodies were butchered with machetes. Video of the mutilated bodies was sent to a girlfriend of one of the victims.

Soon after Attorney General Jeff Sessions visited Central Islip and vowed publicly to combat MS-13. "We are targeting you, we are coming after you," he said.

Law enforcement efforts appear to be bearing fruit. Thirteen suspected members of MS-13 were indicted in March on murder charges related to seven killings on Long Island over the past three years -- including those of the Brentwood teens. And last week, federal prosecutors brought a new 59-count indictment that includes charges against four suspects in the brutal April slayings.

"MS-13 is our number-one priority on Long Island because much of what they do and how they behave boils down to violence for violence sake," said William F. Sweeney, Jr., head of the FBI's New York field office, last week.

"The drugs they're accused of selling (are) almost an excuse to retaliate and attack rivals, or others who cross them," Sweeney added. "The idea that human life means nothing to these gang members should shock the conscience, and we cannot allow this type of thinking to take hold in our youth."

The gang mostly targets Central American immigrants, many who came to the US seeking refuge from gang violence back home in El Salvador, Guatemala and Honduras only to find themselves in danger again.

"We're seeing that they're targeting some of the most recently arrived youths who are coming into families who are in transition with their immigration status. Young people who don't know a lot of people in the community, and who are easily targeted and scared," said Barrientos of Make the Road.

Evelyn Rodriguez, mother of Kayla Cuevas, 16, who was brutally slain last year -- allegedly by members of MS-13 -- weeps outside a courthouse in Central Islip in March.

"They come here, largely without conventional family, whoever their sponsor may be, maybe a family member, maybe someone they don't even know," said Det. Sergeant Michael Morino, commanding officer of the Nassau County Police Department's gang investigation squad.

"They go to a school district not speaking the language and they're in a new country so they are very vulnerable and these gangs preach protection," Morino said. "And that's a powerful recruitment tool."

'I felt safe with them'

David and Alex are just 16 and 17, but they have already been MS-13 gang members for three years.

The two, who don't want their real names used out of fear for their safety, live in Hempstead, New York, where they recently agreed to meet late at night for an interview.

David, who was born in the US to parents from El Salvador and Mexico, said he had no choice but to join MS-13 when he was 13. By age 9, he'd already seen someone get shot.

"I started growing up in that type of neighborhood. I didn't really get love from my family. Where I grew up, they (MS-13) were there, almost all of them," he said. "They seemed like really nice people. They were there for me through tough times."

"I had friends that were in gangs so I started talking with them and they started telling me how it would be if I joined, how they would have my back and everything. I felt safe with them," agreed Alex, who was born in Honduras and joined the gang at 14. "If you're not MS-13, you're the target. You know, if you can't beat them, join them. That's what they want."

A memorial candle lies in the grass near where the bodies of four young men were discovered on April 28 in Central Islip. They were beaten with wooden clubs and slashed with machetes.

During their initiation into the gang, the teens each were beaten by three gang members for 13 seconds.

"It's kind of a lesson when you join the gang to see if you're man enough to take the beating," David said. "You want to show them you're not afraid of anything. They're trying to see if you're really man enough to join, man enough to take the beating."

The two teens don't have scars or gang tattoos yet.

"You have to earn them," David said. "They're called battle scars, for the work you put in for the gang, and the beatings, stabbings, and shootings you're taking for them ... those are like trophies when it comes to gangs."

Both say they see the futility of gang life and would like to leave the lifestyle behind. But it's not easy.

"At one point I felt like, damn, why am I in this? Is that what I'm going for? Taking somebody's loved one and hurting them? What if they took somebody from me?" Alex said. "You're not a real man if you're risking your life and risking your family to impress the streets. That's what I want everybody to know," he added. "Impressing the streets isn't going to get you nowhere, honestly."

As for young people who might be thinking about joining MS-13, Alex has a message: Don't.

"You're going to try to leave, you're not going to be able to," he said. "Don't join ... because I know you're going to regret it.

"They're everywhere. You could move anywhere you want. They'll find you."

The Trump effect

It's not clear what Trump will say when he speaks in Suffolk County on Friday. But the President has already been talking about the gang for months, reiterating his promise to arrest and deport them.

"Vicious and disgusting and horrible MS-13 gang members ... we're getting them out," he said in June. "They've gotten rid of 6,000 so far. We're about 50 percent there. And we're actually liberating towns, like on Long Island, where I grew up."

But others, citing ICE deportation figures, have disputed Trump's estimates.

As of late June, ICE data showed 2,798 suspected gang members had been deported so far this fiscal year, which began in October. That figure includes all gangs, not just MS-13.

Trump has adopted a more aggressive stance towards undocumented immigrants. Between late January and late April, his administration arrested an average of 108 undocumented immigrants a day with no criminal record, an increase of about 150% from the same period a year ago.

But Barrientos of Make the Road believes that such increasing immigration enforcement action makes undocumented immigrants more fearful of arrest and deportation, which only helps MS-13.

US Attorney Robert Capers, left, flanked by members of the FBI and Nassau and Suffolk County Police, speaks at a news conference in March. They announced the indictment of suspects in seven gang-related slayings.

"This situation is actually putting people who are very vulnerable in a more precarious situation because then they remain at the mercy of gangs," he said.

Police in Nassau County say immigrants and victims of MS-13, such as Margarita and her son, should still feel safe coming forward.

"I can say without any doubt ... we never, never ask any (immigration) status and we don't care, on victims and witnesses," said Detective Sgt. Michael Morino of Nassau County Police's gang investigation squad.

But the Nassau County District Attorney's office said calls to their Immigrant Affairs Tips Hotline are way down in 2017.

"Because immigrants are scared to call law enforcement, crimes are going unreported, victims are not getting justice, criminals are going unpunished and we are all less safe," says Silvia Finkelstein, the office's director of immigrant affairs.

David and Alex don't disagree.

"They [MS-13] feel like they can do whatever they want, 'cause Trump himself has made everybody fear," Alex said. "He's helping them."