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.

Former Yankees player Brett and his wife, Jessica, announced last month that their teenage son, Miller, died on March 21. Here’s what we know about the cause of his death.