The Department of Homeland Security (DHS) inspector general launched an investigation Friday into the death of a 7-year-old migrant girl who died in Border Patrol custody. The watchdog said it would provide a final report to DHS Secretary Kirstjen Nielsen, Congress and the public.

"In addition to an investigation of the specific circumstances of the child's death, DHS OIG will continue its ongoing program of unannounced inspections of Customs and Border Protection and Immigration and Customs Enforcement facilities. The results of these inspections will also be reported publicly," the statement said.

Senior House Democrats had sent a letter demanding the watchdog to investigate the incident. They also called for an investigation into border patrol's failure to notify Congress about the girl's death until a week later.

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"The investigation should also examine the appropriateness of holding children in Border Patrol stations, which were never designed to hold children," Rep. Jerrold Nadler, chairman of the House Judiciary Committee, wrote in the letter.

Jackeline Caal Handout

The girl, identified by the Guatemalan government as Jackeline Caal, and her father were taken into custody on December 6 around 10 p.m., south of Lordsburg, New Mexico, the Washington Post reported. They were among 163 migrants who turned themselves in at the border.

Homeland Security said she started having seizures more than eight hours later. Her body temperature was recorded by emergency responders as 105.7 degrees. Border Patrol told the Post that she "reportedly had not eaten or consumed water for several days."

She was transported via helicopter to an El Paso hospital, where she died less than 24 hours later. DHS said be autopsy would be performed on the girl.