A U.S. Border Patrol agent has been arrested on an assault charge over accusations he punched a Mexican teenager after confiscating the 15-year-old’s cellphone at an Arizona immigration station, officials said on Friday.

Nogales Border Patrol agent Aldo Francisco Arteaga, 35 turned himself in to the Santa Cruz County Sheriff’s Office on Thursday, U.S. Customs and Border Protection spokesman Victor Brabble said.

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Arteaga’s arrest comes as the Border Patrol said it would test body cameras for its agents following allegations of abuse and use of excessive force. Washington last week gave the agency authority to investigate staff for criminal misconduct.

Agents are facing accusations made in June by immigration activists that more than 100 migrant children mainly from Central America and Mexico suffered sexual assault and beatings and were denied adequate medical care, food and water in U.S. detention facilities.

It was unclear if the boy was connected to that case, nor could the Border Patrol give any details on why he was in custody except to say his detention at Nogales indicated he was likely awaiting deportation proceedings, possibly for entering the country illegally.

The Nogales Border Patrol Station is the largest Border Patrol Station in the United States, tasked with patrolling 1,100 square miles (2,850 sq km) of terrain along the border with Mexico.

Prosecutors have camera surveillance footage from inside a holding cell that they say shows Arteaga punching the boy in the stomach in January after confiscating a banned cell phone, Santa Cruz County Deputy Attorney Liliana Ortega said.

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Arteaga, who joined the agency in 2005, was charged earlier this month with one count of aggravated assault on a minor, Ortega said. Arteaga was to be arraigned in Santa Cruz county court next week, Ortega said.

Ortega said it was possible the boy had since been deported to Mexico but declined to release additional information about him, including whether he was in the facility alone or with family.

Central American children, mostly from Honduras, El Salvador and Guatemala, began flooding the border at crossing points in Texas earlier this year, overwhelming local officials and leading the federal government to send thousands to other states for processing.

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Border Patrol agents have also detained Mexican children who have crossed the border without their parents but they were not a large part of the surge of unaccompanied minors, Brabble said.

(Editing by Cynthia Johnston and Sandra Maler)