To
quote despair.com: "It could be that the purpose of your life is only to serve as a warning to others."
Hopefully others will learn from their tragic mistake. Even something as simple as $20 battery operated CO detector could've saved their lives.
We have both on the boat, the built-in ones and a separate battery operated one. On the few situations when there's been fumes detected sometimes it was one of the built-ins, others it was the residential-grade one. Depended entirely on which hatches were open and the source of the fumes. Causes varied; our generator (open companionway door), adjacent boat's engines during docking at a slip (side hatches open), nearby portable genset (top hatches open). The docking situation wasn't unexpected and dissipated quickly. We moved away from the genset to a different part of the anchorage.