Though there were no visible signs of trauma, Santa Fe County Sheriff Adan Mendoza said the couple’s deaths could have resulted from various causes, including double homicide, suicide, accidental death, or natural causes. Two surviving dogs were also found—one inside the house and another outside.

Forensic expert and Fox News contributor Dr. Michael Baden suggested the deaths were “typical” of carbon monoxide poisoning. He explained that if a car engine is left running without proper ventilation, carbon monoxide from the exhaust can seep into the house, causing both humans and animals to succumb without pain or awareness. He also noted that a boiler malfunction could produce the same deadly gas.

The couple had been married for over 30 years and had lived in their Santa Fe home since Hackman retired from acting in the early 2000s.

Following the discovery of their bodies, authorities applied for a search warrant and brought in the fire department and gas company to ensure the home was safe for further investigation.