Miller Gardner, the 14-year-old son of the longtime Yankees player Brett Gardner, died of carbon monoxide poisoning while on vacation with his family last month, the Costa Rican authorities said on Thursday.
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.
Mr. Zúñiga said that other tests were also performed, including drug tests, but they were all negative. He said the autopsy report found telltale signs of carbon monoxide poisoning on the organs, and added that the case could be considered closed.
Miller and his family were staying at a resort in Costa Rica. The family said in a statement released through the Yankees last month that Miller had died on March 21 “after falling ill along with several other family members while on vacation.”
“He passed away peacefully in his sleep,” the family said.
The authorities said the family was staying in Manuel Antonio, a resort area on the central Pacific Coast of Costa Rica.
The authorities said at a news conference on Wednesday that the family’s room at the resort was next to a room with machinery and said that contamination may have occurred as a result.
The resort where the family stayed, Arenas Del Mar Beachfront & Rainforest Resort, did not respond to a request for comment after the toxicology results.
The family said Miller “loved football, baseball, golf, hunting, fishing, his family and his friends.”
Brett Gardner, 41, played for the Yankees for his entire major league career from 2008 to 2021.
He played left and center field and was part of the Yankee World Series championship team of 2009. By 2019 he was the last remaining Yankee from that team, which was the last to win the title.
A speedy left-handed hitting player, he led the league in stolen bases in 2011 and triples in 2013. His lone All Star season came in 2015. For his career, he hit .256 with 139 home runs.
He scored the final run in the old Yankee Stadium in 2008.
Mr. Gardner and his wife, Jessica, reside in South Carolina. They have another son, Hunter, who is 16.
Jonathan Wolfe contributed reporting.
