Brett Gardner‘s 14-year-old son Miller may have died from carbon monoxide poisoning, Costa Rica’s Judicial Investigation Agency (OIJ) announced Monday.

OIJ Director Rándall Zúñiga revealed via a press briefing high levels of carbon monoxide were detected in the Gardner family’s hotel room at the Arenas Del Mar Beachfront & Rainforest Resort in Manuel Antonio.

Zúñiga also noted in his native Spanish language that the family’s room was located next to “a specialized machine room” which may have caused the contamination … leading Miller to inhale a fatal amount of “these highly dangerous gases.”

Miller died in his sleep on March 19 after he and other members of his family had fallen ill. At first, officials thought he might have died from asphyxia because his body was found with vomit on it.

When that was ruled out, investigators suggested he may have had a severe case of food poisoning.

The OIJ has been working with the United States FBI to investigate Miller’s death. The investigation is still open as officials wait for the final toxicology results. Therefore, no official cause of death has been confirmed.