• Brett Gardner’s son Miller’s cause of death was ruled to be exposure to carbon monoxide
• Miller passed away while on vacation with his family in Costa Rica on March 21, 2025
• Arenas Del Mar Beachfront & Rainforest Resort, the hotel where Miller and his family were staying, previously refuted claims that there were “high levels of carbon monoxide contamination” in the room

The official cause of death for New York Yankees player Brett Gardner’s son Miller has been released.

On Wednesday, April 2, the cause of death for the 14-year-old who tragically passed away while his family was on vacation in Costa Rica was ruled to be exposure to carbon monoxide.

Miller tested for carboxyhemoglobin, Randall Zúñiga, director of Costa Rica’s Judicial Investigation Department (OIJ), told the Associated Press, via translation. Per Medscape, carboxyhemoglobin is “a stable complex of carbon monoxide that forms in red blood cells when carbon monoxide is inhaled.”

A carboxyhemoglobin saturation level of over 50% is considered lethal. Miller’s was 64%, Zúñiga said, per the AP. A “layer” was also found on Miller’s organs during the autopsy, indicating the poisonous gas was present.

“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 continued.

Last Monday, Arenas Del Mar Beachfront & Rainforest Resort, the hotel where Miller and his family were staying, refuted the agency’s findings of “high levels of carbon monoxide contamination,” saying that the levels of carbon monoxide in the room were “non-existent and non-lethal.”

PEOPLE reached out to the hotel on Wednesday for comment on OIJ’s cause of death findings.

Never miss a story — sign up for PEOPLE’s free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer​​, from celebrity news to compelling human interest stories. 

In March, the MLB team shared news of Miller’s death in a statement via X on behalf of his mother and father.

“With heavy hearts we are saddened to announce the passing of our youngest son, Miller. He was 14 years old and has left us far too soon after falling ill along with several other family members while on vacation. We have so many questions and so few answers at this point, but we do know that he passed away peacefully in his sleep on the morning of Friday, March 21st,” the post read.

His parents remembered Miller as “a beloved son and brother,” known for “his infectious smile.”

“We are so thankful to all who have reached out to offer support and encouragement during this difficult time and we are confident our faith, family, and friends will help us navigate this unimaginable loss. Our prayers go out to Miller’s teammates and friends, as well as to all other families who have lost a child far too soon as we share their grief,” the family added, asking for privacy as they grieve.

Later that month, officials ruled out asphyxiation as the cause of death for Miller after it was initially reported that he died “after a possible intoxication after apparently ingesting some food,” according to NBC News.

At the time, Juan Pablo Alvarado Garcia, an official with Costa Rica’s Judicial Investigation Agency, said that it may take up to “two to three months” before autopsy results come in for the teenager.

“The results are expected to be available in two to three months, due to the high demand for autopsies being performed in the country, resulting from the increase in homicides,” Garcia said.

“The case is being investigated by agents from the Quepos and Parrita OIJ Sub-Delegation and is currently being handled as a death under investigation,” he added.

On March 31, a video statement from Zúñiga was posted on the agency’s YouTube account that said that while the investigation remained ongoing, a “hazardous atmospheres” team conducted tests in the room his family was staying in.

“At that time, high levels of carbon monoxide contamination were detected in that room. Which then leads us to a line of investigation in which it appears that this person may have died from inhaling these very dangerous gases,” he said.

“In this regard, it is important to note that adjacent to this room, there is a specialized machine room, which is believed to contain some type of contamination in these rooms, and this could have caused some kind of contamination at the time,” continued Zúniga.