"They just didn't believe they were real. They kept telling him they were fake," Galan told the Post. "He's been here all his life."
Marlon agreed to be voluntarily deported to Mexico within days of his detention, according to the Morning News.
"I didn't imagine this could happen, and now I'm so sad that I'm not with my family," Marlon told the newspaper by phone from Reynosa, Mexico, where he's staying with family. "Now, we just have to wait and see and hope that they release my brother."
Galicia was born in December 2000 at Parkland Memorial Hospital in Dallas, according to a birth certificate reviewed by the Morning News. Galan told CBS News that she's provided U.S. Immigration and Customs Enforcement officials with several documents to prove Galicia's American citizenship, including his birth certificate, health insurance cards and high school ID.
"He's going on a full month of being wrongfully detained," Galan told the Morning News. "He's a U.S. citizen, and he needs to be released now."
According to the Post, authorities might not have been able to immediately confirm the authenticity of Galicia's paperwork because his mother, who is not a U.S. citizen, took out a tourist visa in his name when he was younger, which falsely listed his place of birth as Mexico. Galicia's mother, Sanjuana, told the Post she got the visa because she believed it was the only way to allow her son to travel across the border to visit family and added that she couldn't get him a U.S. passport because she gave a different name for herself on her son's birth certificate.
Sanjuana told the Post that her son is "desperate" to leave detention and that he fears he might be deported to Mexico at any moment.
"I need my son back," she told the Morning News. "I just want to prove to them that he is a citizen. He's not a criminal or anything bad. He's a good kid."
It's not the first time authorities have detained a person claiming American citizenship, though the cases make up a fraction of ICE detentions each year, according to a 2018 report from the Los Angeles Times.
Between 2012 and April 2018, ICE officials released 1,480 people from custody after investigating their claims of American citizenship, the Times reported. A review of Justice Department records and interviews with immigration attorneys "uncovered hundreds of additional cases in the country's immigration courts in which people were forced to prove they are Americans and sometimes spent months or even years in detention," the newspaper reported.