The Guatemalan sisters had managed to reach the Texas border by bus last July when they got lost.“Thankfully, or so we thought, we spotted two U.S. immigration officers and asked them for help,” the older sister, then 19, wrote in an essay.

The Customs and Border Protection officers drove the 19-year-old and her sister, then 17, to a field office in Presidio, Tex., where they were placed in a holding cell and left with one officer. Then, one by one, the officer took the sisters into a windowless space that looked like a pantry or closet. They say he locked them from leaving, forced them to strip down and fondled their private areas.

The American Civil Liberties Union of Northern California filed legal claims Tuesday against Customs and Border Protection on behalf of the sisters, who were not identified, but now live in Fresno with their mother. The federal tort claim is seeking $750,000 in compensation for each sister.

A representative of the agency told the Los Angeles Times it can’t comment on pending litigation, but added, “We take allegations of misconduct seriously and there is no room in CBP for the mistreatment or misconduct of any kind toward those in our custody.”

The federal authorities have not pursued criminal charges against the officer, who was not identified.

On that day in July, the officer first took the older sister aside, according to the lawsuit. He ordered her to remove her sweater, shirt and tank top to make sure she “wasn’t carrying anything illegal,” the woman wrote, and then began to run his hands over her bra. He lifted the bra, placing his hands inside and touching her bare breasts.

Then, according to the complaint, he forcibly pulled down her leggings to her knees. As she begged him to allow her to keep on her underwear, he pulled them down and touched her genitals with his hands.

The woman was allowed to return to her cell about 5 to 7 minutes later. She cried as she saw the officer take her sister, then 17, into the same pantry to commit the same conduct.

“My sister is just a kid — I never thought he would do to her what he did to me,” the older sister wrote in a blog post. “To this day I still can’t believe it. I feel so guilty.”

As the two sisters cried in their holding cells afterward, the unnamed officer tried calming them down by offering them chips and chocolates, the older sister recalled. He asked that they not tell anyone about what happened, and in exchange, offered to allow the younger sister to pass as a minor. But the sisters did not respond to the offer, and did not oblige with his request.

They reported the abuse shortly after to another immigration officer in the same field office, and the Department of Homeland Security’s Office of Inspector General launched an investigation. The sisters were interviewed twice and asked to draw a depiction of the space where they said the incident happened.

“I was so scared and confused — I couldn’t understand why he was doing this,” the older sister wrote. “It clearly wasn’t necessary for security purposes. Now that I look back, I feel so stupid that I let it happen. And I now realize it was all for his own enjoyment.”

The two sisters’ mother has lived in the United States for 12 years. Both of the girls have been attending weekly counseling sessions with a counselor due to the “emotional distress” they suffered during the alleged sexual assault.

“The shame and hurt we felt in that room are indescribable,” the older sister wrote. “The thought of an immigration enforcement officer touching my most intimate body parts without my consent breaks me. I have suffered every day from this experience that it has been extremely hard to sleep at night. There have even been some days when I feel like I shouldn’t be alive.”

A 2014 Los Angeles Times investigation found that the vast majority of complaints involving Border Patrol agents for alleged beatings, sexual abuse and other mistreatment of detainees on the Southwest border resulted in no disciplinary action. From 2012 to 2014 more than 35 sexual misconduct cases were pursued against agents, the agency’s former head of internal affairs revealed to CBS News.

When the two girls fled Guatemala, they knew arrest and deportation were a possibility, the older sister wrote, but for the first time in many years “we felt confident that no one would hurt us.”

“We thought we had left a world of violence and oppression,” the older sister wrote, “only to realize immigration enforcement officers in the United States appeared to be no different than law enforcement in our home country, abusing the tremendous power and responsibility that comes with their job.”