The reason why actor Gene Hackman, his wife, and their dog passed away may be quite mundane. His daughter was the first to comment on the matter, suggesting that carbon monoxide poisoning could have been the cause while talking to TMZ.
However, a special investigation has already ruled out this theory. The New Mexico Gas Co. tested the gas lines in and around the home after the bodies were discovered, but no issues were found. Additionally, the Fire Department found no signs of a carbon monoxide leak or poisoning.
A detective noted that while there were no obvious signs of a gas leak, exposure to gas or carbon monoxide might not always leave visible traces.

Nevertheless, despite the sheriff officially stating that the deaths were non-violent, detectives from the Santa Fe County Sheriff's Office wrote in a search warrant that investigators found the deaths “suspicious enough in nature to require a thorough search and investigation.”
Actor Gene Hackman, 95, and his wife, Betsy Arakawa, 64, were found dead in their home in Santa Fe, New Mexico, along with their dog. A welfare check was done after neighbors and a maintenance worker became concerned.
Investigators found no signs of forced entry or injuries. However, prescription pills were found near Arakawa, and some details seemed unusual, leading detectives to treat the case as suspicious.

Hackman, a two-time Oscar winner known for The French Connection and Unforgiven, had retired from acting in 2004. The couple, married since 1991, lived a quiet life. Many in Hollywood, including director Francis Ford Coppola, have shared tributes, calling Hackman a brilliant actor.