Already done. CO was ruled out.They didnt detect carbon monoxide when they tested , but that was nine days later. The autopsy will be the answer .
"Preliminary autopsy results didn’t determine how Oscar-winner Gene Hackman and his wife died at their home in Santa Fe, New Mexico, but did rule out that they were killed by carbon monoxide poisoning, the sheriff leading the investigation said Friday."
"Carbon monoxide can be ruled out since it can dissipate from the environment but not from a body, renowned medical examiner Dr. Michael Baden said."