Unaccompanied children who crossed the United States-Mexico border in a surge of immigration from Central America between 2009 and 2014 were routinely beaten and sexually abused by Border Patrol agents, according to a new report.

Some 30,000 documents obtained from the Department of Homeland Security (DHS) via a Freedom of Information Act request describe hundreds of incidents of physical abuse against children in the custody of U.S. Customs and Border Protection (CBP), according to the report released Wednesday (May 23) by the American Civil Liberties Union (ACLU).

One quarter of the children interviewed reported cases of physical abuse, including sexual assault, and more than half reported verbal abuse including death threats, per the report. Half of the children interviewed also said they were denied medical care, while 80 percent reported inadequate provisions of food and water.

The cases highlighted by the ACLU include a 16-year-old who said a Border Patrol agent smashed his head on the ground with his boot, and a handcuffed 15-year-old who was punched in the mouth by a Border Patrol agent and then denied medical care. Several other minors reported being hit with stun guns, though they were not resisting arrest.

“At best, this abuse amounts to unprofessional, degrading mistreatment of vulnerable minors. At worst, the abuse amounts to unlawful and potentially criminal misconduct by federal immigration officials,” the report says.

Once in detention, some children reported seeing other minors sexually abused by border guards. “A 15-year-old witnessed a male Border Patrol agent sexually abusing another female detainee,” the report says. “A few days later, the same agent inappropriately touched the 15-year-old.”

Other children reported being threatened with sexual assault and rape. Said one child, according to the documents obtained by the ACLU: “The female officer threatened me. She said that if I did not say the truth about my age I would become the wife of a Black male detainee and the other detainees.” Other children reported being held in frigid holding blocks, some forced to sleep on concrete floors.

“The [Office for Civil Rights and Civil Liberties] documents show that abuse occurs at each stage of a child’s interaction with CBP, from apprehension to detention to deportation,” the ACLU report says.

CBP labelled the ACLU report “unfounded” and “false,” saying that the report ignores improvements made by the agency and oversight efforts conducted by independent organizations.

“All CBP employees embody our core values, perform their duties with integrity, and are dedicated to our mission of securing the American people and our borders while facilitating legitimate trade and travel,” the agency said in a statement. “The men and women of CBP perform their duties professionally and treat everyone equally with dignity and respect.”

Despite the alleged misconduct, the DHS documents provide little evidence that the agency has disciplined agents for abusive behavior, according to the report, or that the internal oversight agencies at the DHS, the Office for Civil Rights and Civil Liberties or the Office of Inspector General have offered meaningful accountability.

“The records indicate—at best—cursory ‘investigations’ closed out via boilerplate language rather than through individualized assessments,” the ACLU report says.