At least 16 self-proclaimed MS-13 gang members were transferred out of federal custody and into community placement centers across the country during the border surge in unaccompanied children from Central America in 2014, according to a new letter from the Chairman of the Committee on Homeland Security and Governmental Affairs.

It was unclear what happened to the members of Mara Salvatrucha, one of the most brutal transnational gangs in the world, and that’s why Senator Ron Johnson, R-Wis., wrote the Office of Refugee Resettlement on Tuesday demanding answers.

In 2014, the Obama Administration declared a humanitarian crisis after tens of thousands of immigrants flooded across the United States border.The dramatic increase in immigrants from El Salvador, Guatemala and Honduras overwhelmed border authorities at the time.

Fox News has now learned that more than a dozen teenage gang members were captured during the surge. According to Johnson’s letter and documents obtained by Fox News, the gang members “freely admitted” that they were “active MS-13 gang members” and marked bathrooms inside a placement center in Nogales, Arizona with MS-13 associated graffiti.

One teenage gang member stated he “was a drug dealer” and “would continue to do the same in the United States with his family.” Another admitted he was a member of the Surenos gang and had been “involved in multiple robberies, assaults and drug dealing” since he was 15 years old.

“These documents appear to show that the federal government knowingly moved self-identified gang members from Nogales, Arizona to placement centers in communities across the country. As you know, it is common for UACs (unaccompanied children) to be released from their placement center while awaiting a court date. It is unclear from these July 2014 documents whether any of these self-identified UAC gang members were released,” Johnson wrote in his letter to the Office of Refugee Resettlement.

Johnson is now asking for a complete accounting of all UACs captured at the border who have self-identified as gang members since 2010.

He also wants to know if any of the gang members were released into communities in Virginia, Washington, Texas, New York and Oklahoma. The questions come as the Committee on Homeland Security and Governmental Affairs holds hearings this week on the "The Rise of MS-13 and Other Transnational Criminal Organizations".

A spokesperson for the Administration for Children and Families told Fox News in a statement, "The Department of Health and Human Services (HHS) Office of Refugee Resettlement (ORR) is reviewing Senator Ron Johnson’s request. As a matter of policy, the HHS Administration for Children and Families (ACF) does not comment publicly on congressional requests before providing an official response to Congress."

A spokesperson for the U.S Customs and Border Protection told Fox News the agency is "required by law to turn all unaccompanied children over to Health and Human Services. CBP protocols require agents to report gang affiliation of juveniles in the system used for processing, and share that information with Immigration and Customs Enforcement within three hours of a request for the juvenile’s placement with HHS’s Office of Refugee Resettlement."