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.

Carbon monoxide is known as the “invisible killer” because it is a colorless, odorless, tasteless gas or liquid

After Brett Gardner’s son Miller Gardner was found dead due to carbon monoxide exposure during a vacation in Costa Rica, a CO forensics investigator explained why his family didn’t face the same fate.