U.S. Sen. Elizabeth Warren, D-Massachusetts, urged the Trump administration Friday to investigate the recent death of an 8-year-old Guatemalan boy, who had been held in Customs and Border Protection custody.

The Massachusetts Democrat, who has been a vocal critic of the White House’s immigration policies, sent a letter to U.S. Department of Homeland Security Acting Inspector General John V. Kelly requesting that he look into the Christmas Eve death of Felipe Alonzo Gomez.

Noting that Gomez’s death marks the second involving a child in CBP custody in December, Warren urged the IG to expand an ongoing probe into the passing of 7-year-old Jakelin Caal to include the circumstances surrounding the most recent fatal incident.

The senator, who noted that she wrote to the IG after Caal’s passing, argued that such deaths are even more concerning given DHS Secretary Kirstjen Nielsen’s recent claim that she did not have “an exact figure” on the number of individuals who have died in U.S. custody.

“In light of these pressing questions, I reiterate my request from earlier this month that you conduct a rigorous and broad investigation and publicly release the results as quickly as possible,” she wrote.

Pointing to reports that Gomez died days after he was detained and transferred to the El Paso and Alamogordo Border Patrol Stations, Warren noted that “experts have raised particular concerns about detaining children at the border in ‘overcrowded, often cold facilities.’”

“Children are not supposed to be held in CBP facilities for more than 72 hours, but it appears that Felipe was shuttled between CBP facilities for six days between his detention on Dec. 18, 2018 and his death on Dec. 24, 2018,” she said. “It is unconscionable that children seeking asylum are dying in U.S. custody.”

Warren argued that with the full circumstances surrounding Gomez’s death unknown, it’s urgent the IG determine how and why he died in CBP custody, as well as whether the agency or any other officials are responsible for his death.

She urged Kelly to, among other things, examine: the specific circumstances of Gomez’s death; what CBP policies and procedures for health screenings and treatment applied to Gomez and were followed; and whether officials were warned of health and safety risks to detained children prior to the two December deaths.

The Associated Press reported that Nielsen, in response to the two deaths, asked the Coast Guard to study CBP’s medical programs and announced that children entering into the such custody will receive “more thorough” assessments.