The 8-year-old boy who died in Border Patrol custody on Christmas Eve had the flu​

The young Guatemalan boy who died in U.S. Border Patrol custody on Christmas Eve tested positive for the flu, officials with the New Mexico Office of the Medical Investigator said Thursday.

It’s still unclear, however, exactly what led to the 8-year-old’s sudden death after two visits to the hospital just days after he was arrested on Dec. 18 at the border in Texas with his father.

“While this result indicates that the child had influenza, determining an accurate cause of death requires further evaluation of other laboratory specimens and interpreting the findings in the context of the symptoms and autopsy findings,” officials cautioned in Thursday’s news release. Four days after they were first detained, the boy, Felipe Gomez-Alonzo, and his father were transferred from a border patrol station in Texas, which was experiencing capacity issues, to another center in New Mexico.

Soon after the transfer to New Mexico, a processing agent noted on Dec. 24 that Felipe was “coughing and appeared to have glossy eyes.” He was sent to a local medical center, diagnosed with a cold, and was set to be released when medical personnel realized he was running a 103-degree fever.

Still, Felipe was discharged into Border Patrol’s care with prescriptions for an antibiotic and Ibuprofen. Border Patrol agents fed Felipe and his father, gave Felipe a dose of his medication and offered further medical assistance when he began to vomit, which Customs and Border Protection said the father declined because his son appeared to be improving.

Later that evening, however, Border Patrol sent Felipe back to the hospital when he continued vomiting. He died within 45 minutes of his second hospital visit.

During the autopsy, investigators said that cheek and nose swabs tested positive for influenza B.

Felipe was the second Guatemalan child to die in Border Patrol custody this month; Jakelin Caal Maquin crossed the border with her father on Dec. 6 and died at an El Paso hospital with liver failure, dehydration, and shock two days later.

U.S. Secretary of Homeland Security Kirstjen Nielsen is scheduled to head to El Paso Friday to review Border Patrol’s methods for medical screening as well as conditions at nearby stations. House Democrats have vowed to investigate Nielsen’s agency and the circumstances that may have led to the deaths.

Nielsen also said Wednesday that several federal agencies will help U.S. Customs and Border Protection to improve care for those held in federal facilities, and Nielsen directed her agency to “extraordinary protective measures” — like changing certain medical policies — in a statement.

Cover image: This Dec, 12, 2018 photo provided by Catarina Gomez on Thursday, Dec. 27, 2018, shows her stepbrother Felipe Gomez Alonzo, 8, near her home in Yalambojoch, Guatemala.(Catarina Gomez via AP)