An eight-year-old boy from Guatemala died early on Christmas Day while he was in the custody of the U.S. government. It marks the second death of a migrant child while detained by U.S: Customs and Border Patrol this month. The boy, who died shortly after midnight Tuesday, showed “signs of potential illness” Monday was taken to a hospital in New Mexico.

The boy, who has not been publicly identified, was diagnosed with a cold although he was later found to have a fever and was held for an additional 90 minutes. He was later released with prescriptions but his illness worsened Monday night, U.S. Customs and Border Protection said in a news release. He threw up and was taken back to the hospital, where he died a few hours later.

Here is the full press release. pic.twitter.com/8bv3xNizF1 — Silvia Foster-Frau (@SilviaElenaFF) December 25, 2018

The cause of the boy’s death is still not known and Customs and Border Patrol vowed to carry out a thorough investigation.

This death comes mere weeks after Jakelin Caal, a seven-year-old from Guatemala, died of dehydration and shock shortly after she was picked up by border agents. Her body was returned to her family’s village Monday. Felipe González Morales, the U.N.’s special rapporteur on the human rights of migrants, has called for a thorough independent investigation into Caal’s death. “When a person, especially a child, is in the custody of a state, that state has to ensure their rights,” González told the Guardian. “States have an obligation to care for migrants who arrive at the border, they cannot treat them as animals in inhuman conditions. I’m not saying this happened in this case, but the U.S. has a duty in this regard.”