SAN JOSE, Costa Rica — Carbon monoxide poisoning was the cause of death of the teenage son of former New York Yankees outfielder Brett Gardner, authorities in Costa Rica confirmed Wednesday night.

Randall Zúñiga, director of the Judicial Investigation Agency, said they tested the 14-year-old Miller Gardner for carboxyhemoglobin, a compound generated when carbon monoxide binds to hemoglobin in the blood.

When carboxyhemoglobin saturation exceeds 50%, it is considered lethal. In Gardner’s case, the test showed a saturation of 64%.

“It’s important to note that adjacent to this room is a dedicated machine room, where it’s believed there may be some type of contamination toward these rooms,” Zúñiga said.

The head of the Costa Rican judicial police added that, during the autopsy, a “layer” was detected on the young man’s organs, which forms when there is a high presence of the poisonous gas.

Miller Gardner died on March 21 while staying with his family at a hotel on the Manuel Antonio beach in Costa Rica’s Central Pacific.

Asphyxiation was initially thought to have caused his death. After an autopsy was performed by the Forensic Pathology Section, that theory was ruled out.

Another line of investigation was into whether the family had suffered food poisoning. Family members had reported feeling ill after dining at a nearby restaurant on the night of March 20 and received treatment from the hotel doctor.

Brett Gardner, 41, was drafted by the Yankees in 2005 and spent his entire major league career with the organization. The speedy outfielder batted .256 with 139 homers, 578 RBIs, 274 steals and 73 triples in 14 seasons from 2008-2021.