Carbon Monoxide seems possible. They had a rustic home with fireplaces. Architecture Digest did a feature on it. He designed/restored homes as a sort of hobby.
Seems plausible they all contracted an illness which rapidly floored them. The D1.1 strain of H5N1 recently spread to cows there and it isn't like normal Flu and Covid have gone away. Worst flu season in 15+ years in the US. Hackman was 95 and his wife was in her 60's. Doesn't take much at that age.
@peter H5N1 is notable for infecting a wide variety of mammalian species including dogs and dogs have already been documented to have died from it. You also have recent studies suggesting cross-infection between owners and their pets.
There's also a strain of H5N1, the D1.1 sub-strain, which has been more associated with severe human infections than the strain widely seen in dairy cows in cattle. The D1.1 strain appears to have made the jump to cows in New Mexico in the last few months.
@peter If you search the Aphis databases, you'll see that New Mexico has a large number of documented infections in wild birds and mammals, many of which are dog contacting. Dog scavenges a bird, gets in a tousle with a skunk, raccoon, etc. those are all ways for it to get infected (to say nothing of raw pet food). NM has also had at least some documented trouble in their poultry and dairy industries this last year. For all we know, they drank some raw milk, ate undercooked eggs, etc.
@peter Doesn't necessarily have to be H5N1, either. Whole bunch of contagious disease which might explain the 3 at once situation. It used to not be uncommon for contagious diseases to silently kill whole families. One of my grandmothers never knew one of her uncles because the whole family all died (probably within days of each other) in their home one winter. Only one survived and he went down to Texas and settled in Galveston just in time for the hurricane.
@Infoseepage H5N1 is not 100% lethal, very much less than that. what you are describing is possible but in the sense that it's possible for two people and a dog to all die from falling off ladders at the same time.
@peter Some diseases kill the elderly fast. Maybe the dog didn't die of what the two of them had and instead simply starved because of a closed household. We don't know how long they were out of contact, just that someone eventually asked for a welfare check.
I'm just saying it could be a lot of things, not just carbon monoxide poisoning (although that seems to fit the very few available facts well too).
Wonder if there will be a public determination of cause of death. Not sure on local laws.
@peter USA today is reporting that Hackman was found dead in the house's mudroom after an apparent fall. His wife was found in a bathroom with a significant number of loose pills and pill bottles around her. Dead dog was locked in a closet. There were other live dogs as well. No signs of carbon monoxide/gas leak reported.
Speculative guess? Hackman had a heart attack or something of that nature and Arakawa killed herself in grief.