Sorry, too busy today to post a bunch of links, and stuff, but knowing the reports say little or no CO found in Hackman's blood is totally bogus, IMHO. Those of you who know this stuff better than me, please set me straight.
In the never ending "World According to Dave '86", carbon monoxide (CO) poisoning occurs because a high enough percentage of the hemoglobin sites in the blood are taken over by CO. Normally it is hemoglobin that takes oxygen from the lungs and distributes it around our bodies. Well, the problem with CO is that it binds stronger to the hemoglobin than oxygen does. Like 200 times stronger. So, it takes CO a long time to disconnect from hemoglobin.
So, we die from CO poisoning because what little CO is in the air attaches itself to our hemoglobin, keeping those hemoglobin sites from distributing oxygen to our bodies. Over time the percentage of hemoglobin bound to CO keeps going up, so people (and animals like dogs) essentially suffocate and die from insufficient oxygen.
If you believe that, then... Hackman and his wife were laying around dead for about 9 days before they were discovered. How much time does the hemoglobin need to release all the carbon monoxide to their body's tissue? The half-life is something like 30 minutes to 2 hours. Just because they're dead doesn't mean the CO will now stay stuck to the hemoglobin indefinitely. I'm no expert on this, but I have to think that in a couple of days after they died all the carbon monoxide had separated itself from the hemoglobin and was absorbed by the tissue of their bodies.
So, there was no carbon monoxide in Hackman and his wife blood when they were discovered.
I believe they dies from carbon monoxide poisoning.