Very sad news, no matter the reason....And I have to say I don't think the conspiracy theories are warranted...I know how police operate in suicides and it incredibly private.
More specifically, they are private precisely because they need to accomplish two major objectives, if it is a suicide.
1. Eliminate any possible external source of the death, i.e., homicide or accidental death. This sometimes takes time, and requires an in-depth autopsy lasting for hours. For carbon monoxide poisoning, there are specific signs that are relatively easy for a forensics investigator to determine if the deaths were consensual, or if the victims were set up by an external source.
A proper autopsy, for instance, would indicate if the victims had suffered poisoning in another location, then transferred to the target location. Such a finding would immediately raise the red flags. Other indicators can be found if evidence of force or assault could be found on the body or bodies of the victims.
2. Once the death is determined to be a suicide, then they are very careful in how this information is disseminated to the press in deference to family privacy and sensitivities.
If step 1 does not conclusively rule out eternal sources for death, then the case remains open, and further tests may be warranted.
NOW: This is not disrespect to the families. As stated before, mutual marital double-suicides are extremely rare, and with the potential problems of the industry as a whole, would immediately raise my own radar if I were an investigator.