I've been thinking CO poisoning, too. One news report said they didn't find any at the time the bodies were found, but it could have dissipated. I know it has a cumulative effect, so relatively small doses can build up in the bloodstream over time, but I don't remember how long it takes to leave the blood, or if it does after death or not.
Maybe toxicology reports will find something. It's very strange. I'm assuming they both had to have collapsed within a pretty short period of time.
Aries
~Sign of the Rams
