An 8-year-old Guatemalan migrant boy died shortly after midnight on Tuesday after being detained by US border agents, the US Customs and Border Protection (CBP) said, making him the second migrant child this month to die in US detention—on the Mexico-US border, Reuters reported.

The boy and his father were in CBP custody on Monday when a Border Patrol agent noticed the child showing signs of illness.

The father and son were taken to the Gerald Champion Regional Medical Center in Alamogordo, New Mexico, where the boy was diagnosed with a common cold and fever, and eventually released by hospital staff.

But later that evening, the boy began vomiting and was transferred back to the hospital. He died there shortly after midnight, CBP said, adding that the official cause of death is not known.

The boy’s death followed the death in early December of 7-year-old Jakelin Caal, also from Guatemala. She died after being detained along with her father by US border agents in a remote part of New Mexico.