Miller Gardner, the youngest son of former New York Yankees outfielder Brett Gardner, died at the age of 14 while on vacation with his family.

Costa Rica authorities confirmed that carbon monoxide poisoning was the cause of death of Miller Gardner, the 14-year-old son of former New York Yankees outfielder Brett Gardner.

A toxicology report after his death found high levels of carboxyhemoglobin, an indicator of carbon monoxide in the blood, according to a statement from Randall Zúñiga, the director of the Costa Rica Judicial Investigation Agency. Miller Gardner’s test showed a saturation of 64 percent, he said, adding that anything over 50 percent was lethal.