Domestic abuse is so sad and so complex to understand. While we don't know that this was not an isolated event, I think it unlikely that without any other violence in the relationship, this man killed his wife. Statistically, vacations tend to provide a brief hiatus from domestic abuse with many partners reporting that it was the only time in their relationship that they felt safe.
All we can do is continue to pray for her family and for every other victim of domestic violence and to continue to push for more victims rights and increased penalties for the abusers.
It sounds like CCL did a great job in keeping the scene well preserved and in contacting the appropriate authorities. I'm sure they wish that people would just stop dying while cruising on their ships.