The surge of unaccompanied minors from Central America at the U.S.-Mexican border has caused more than administrative headaches — it is bringing gang violence to the American heartland, an immigration researcher said Friday.

The Center for Immigration Studies, which favors lower levels of immigration, released a pair of studies pointing to tens of thousands of children that federal authorities have lost track of after temporarily placing them in the United States. Thousands of those youths have joined the violent Central American gang Mara Salvatrucha, or MS-13, according to the studies.

“The residents feel like they’re under siege.”

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Many have ended up in Suffolk County on Long Island, New York. One of the reports released Friday cites a September story in the Long Island Press estimating that Suffolk County, alone, has had more than 1,000 MS-13 members over the previous decade. The Associated Press reported last month that the gang is responsible for some 30 homicides on Long Island since 2010. Authorities have arrested 35 alleged gang member just in the last several weeks.

Lenny Tucker, president of the Brentwood Association of Concerned Citizens in Suffolk County, told reporters on a conference call that extreme violence has struck the community.

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“The residents feel like they’re under siege,” he said.

Tucker became a community activist in 2009 after three “gang-member wannabes” on an initiation drove to his block and fired randomly at his house. At the time, Tucker’s 13-year-old son was having a gathering of friends. One of them, 13-year-old Christopher Hamilton, took a fatal shot to the temple.

“I had about 19 teenagers at my house that were traumatized,” he said. “I have to live with the fact that my house is now a crime scene.”

The Center for Immigration Studies report quoted Pedro Sanchez, consul for the government of El Salvador in New York City, as saying that American communities need to be more vigilant against the threat posed by gang violence imported from Central America.

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“Communities are not prepared here in the United States for gang violence,” he said. “If they don’t pay enough attention to their youth it will get worse.”

Gang violence is a persistent problem across the country. According to Immigration and Customs Enforcement officials, federal prosecutors convicted 250 gang members between 2003 and 2015 of a variety of charges. From 2010 to 2015, prosecutors convicted 35 gang members in connection with 20 homicides.

[lz_table title=”MS-13 Arrests, 2005-2014″ source=”Center for Immigration Studies”]ICE Office,Arrests

Washington D.C. (includes Va.),635

Baltimore,416

Long Island,292

Los Angeles,204

Charlotte (N.C.),199

Newark (N.J),199

Boston,197

Atlanta,163

Dallas,143

San Francisco,142

Houston,123

Miami,115

[/lz_table]

Joseph Kolb, a researcher who wrote both reports for the Center for Immigration Studies, blamed systemic failures in the U.S. policy toward unaccompanied minors for much of the rising gang violence. Since 2013, more than 200,000 youths have crossed into the United States. Concern over the surge prompted four lawmakers on Thursday to demand a crackdown at the border in a letter to Homeland Security Secretary Jeh Johnson.

He said most are coming out of a mistaken belief that they are eligible for the Deferred Action for Childhood Arrivals (DACA), which shields certain illegal immigrants from deportation.

Kolb cited a 2015 report by the Texas Department of Public Safety concluding that the increase in youths from Central America has exacerbated gang violence, particularly in the Houston metropolitan area.

The agency upgraded its assessment from a Tier 2 to a Tier 1 threat. The report specifically blames the influx of Central Americans since 2014 for swelling the gang’s membership in Texas.

A.J. Louderback, the sheriff in Jackson County, Texas, told reporters Friday that law enforcement officials in the Lone Star State have seen machete attacks, scalpings, killings of 13-year-olds, and other extreme violence.

“We are inexperienced in seeing the level of brutality, savagery, that MS-13 are doing here in Texas,” he said.

When youths from Central America started crossing the border in large numbers in 2014, President Obama’s administration concluded that the William Wilberforce Trafficking Victims Reauthorization Protection Act of 2008 — designed to combat human trafficking — required authorities to place the teenagers with sponsors in the United States.

But Kolb said the vast majority were not trafficking victims but willing participants — often aided by smugglers — in a scheme to come to the United States. Many of the sponsors are themselves illegal immigrants. He pointed to data obtained by the Associated Press indicating that from February 2014 to September 2015, federal authorities placed 56,000 of the youths, or 80 percent, with sponsors who come to the United States without permission.

Another 700 were placed with sponsors who are in deportation proceedings. Only 4,900 children had sponsors living legally in America.

A whistleblower, according to a letter last year to Health and Human Services Secretary Sylvia Burwell by Senate Judiciary Committee Chairman Charles Grassley (R-Iowa) and Sen. John Cornyn (R-Texas), claimed that 3,400 sponsors out of 29,000 listed in a government database at the time had criminal convictions. The crimes ran the gamut from DUI to burglary to child molestation and homicide.

Once placed in the United States, it can take up to five years to determine the asylum claims of the youths. In the interim, the Office of Refugee Resettlement often loses track of them, according to Kolb. His report states that the office makes a follow-up phone call 30 days after the child is placed.

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The report states that in the first three months of fiscal year 2016, only 56 percent of children and 88 percent of sponsors participated in the follow-up call — with the remainder who declined to participate facing minimal consequences.

The report states that Office of Refugee Resettlement spokesman Mark Weber told Kolb that the agency receives a comprehensive evaluation of each child and does not release anyone considered a threat. The report argues that the approach is naïve.

Kolb cites data from the Office of Refugee Resettlement indicating that since 2014, 3,709 unaccompanied minors have been placed in Suffolk County, making it the second most-frequent resettlement destination in the country.