The "bottle of prescription pills were spilled on the table" keeps getting brought up. Any chance it was something simply innocuous, like "nitro-glycerine tablets" or something else that a person might be in a bit of a 'scramble' to get to,,,, when needed?
And whether or not there was CO in the house, and then dissipated, will be shown in the autopsy results because it won't leave a body. It'll still be there, and tissue tests will show.
Usually takes about 35 minutes.
That way there's still time to build the plot a bit more, before the dramatic chase and then confession/explanation of the dramatic event. They seem to be wanting to drag this out into a series/sequel.
(sarcasm font OFF, for now)