The 14-year-old son of former New York Yankees star Brett Gardner may have died from carbon monoxide poisoning, Costa Rican investigators said Monday in another twist to the tragedy.

Tests conducted in a hotel room where the Gardners stayed during their vacation last month showed “high emissions of carbon monoxide contamination,” Randall Zuniga of Costa Rica’s Judicial Investigation Department said in a news conference, ESPN reported. Miller Gardner may have succumbed to “inhaling hazardous gases,” he added.

Investigators figure the source of the contamination was a “machine room” next door.

“Levels of up to 600 parts per million were found, when the correct level should be zero in this specific case,” Zuniga said. Exposure to 200 parts per million or higher can reportedly cause death within hours.

Miller Gardner died on March 21. An emergency team from a nearby urgent care administered CPR for 30 minutes but could not save him.

The entire family felt unwell the previous night after dining at a local restaurant, according to reports. Authorities initially believed the teen died of “asphyxiation due to intoxication related to food poisoning” but later ruled that out.

Investigators are awaiting autopsy and toxicology results. The FBI is aiding in the investigation, Zuniga told ESPN.

Miller Gardner played football and baseball at Pinewood Preparatory School in Summerville, South Carolina.

“The void Miller’s passing leaves in the hearts of his family, friends, teammates, teachers, coaches and others will be felt for years,” a recently published obituary read. “The Gardner family will forever cherish the places they visited, the people they met, the friends they made, and the memories they created together. Miller’s time here with them was brief but his spirit will carry on forever through those who were impacted by the way he lived.”

Brett Gardner played on the Yankees’ 2009 World Series championship team during his 14 seasons as an outfielder in the Bronx.