(CNN) A sick Guatemalan boy who died in government custody was lying on the floor for hours before someone found him dead, a video first obtained by ProPublica shows.

The boy, identified by a US Customs and Border Protection official as Carlos Gregorio Hernandez Vasquez, 16, died on May 20 at a Border Patrol station in Weslaco, Texas, days after he crossed into the US and was apprehended by immigration officials, CBP said.

Surveillance video of a holding cell at the Weslaco facility first obtained by ProPublica and published on Thursday show the last moments of the boy's life. ProPublica analyzed the video and compared it with police and emergency services records to create a timeline. CNN later obtained a copy of the video.

The boy was waiting to be transferred to the custody of the Health and Human Services Department, as is customary for unaccompanied minors, when he was diagnosed with the flu and taken to the Weslaco facility, the CBP official said.

In the video, Carlos first appears walking inside a cell in the Weslaco facility, wearing blue jeans, a dark long-sleeve shirt and a disposable white mask. He lays down on a cement bench as another boy, who was not identified, is sleeping under a Mylar blanket on a bench across from him.

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