Officials have determined what killed the son of former Yankees outfielder Brett Gardner.

Miller Gardner died of carbon monoxide poisoning, officials in Costa Rica have determined.

Judicial Investigation Agency director Randall Zúñiga said the 14-year-old had 64% saturation of carboxyhemoglobin in his blood. The deadly level is 50%.

Zúñiga said that they found a “layer” in his organs, which will form when there is a high amount of carbon monoxide in a person’s system.

No other toxic substances were found.

Investigators conducted tests in the family’s hotel room and found “high emissions of carbon monoxide contamination.”

“Levels of up to 600 parts per million were found, when the correct level should be zero in this specific case,” Zúñiga said.

“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.

Hotel representatives disputed the preliminary findings earlier this week, before the toxicology report was released.

Arenas Del Mar spokesperson Dana Cohen said, “The high levels of carbon monoxide were in a mechanical room that guests do not occupy.”

“The levels in the hotel room were non-existent and non-lethal. There was an error in this initial reporting,” Cohen said on Tuesday. The toxicology report was released on Wednesday.

Miller Gardner died on March 21. He was on vacation with his family at a Costa Rican beach hotel.

At first, officials thought the teenager died from asphyxiation, but that was ruled out during his autopsy. Officials also thought he and his family, who also said they were feeling sick, had food poisoning. A hotel doctor treated the family on the night of March 20.

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