You'll never believe it, but actually experts and professionals have already been studying "these tragedies" for decades now, and even have a pretty darn good idea of what the "commonalities" and causes are. There are thousands of books, studies, scholarly articles, and popular articles already published on exactly this subject. Many Websleuthers have posted links to some of the best of this information. You should really take a look.
Because guess what?
These are NOT "toxic relationships that erupt into murder." These are psychopaths, sociopaths, narcissists... ABUSERS. And to contradict a favorite myth of misogynists the world over, no, abuse victims do not "bring it on themselves." And no, FAs don't annihilate whole families because they were bullied and nagged by their meanie wives and "the mouse roared." If they were really so cowed, wouldn't they just pack a bag and disappear into the night? This whole fairytale scenario pushed by incels and MRAs simply does not hold up to logic or basic Psych 101.
Oh and yes, a man who kills two precious preschoolers who call him their hero and stuffs them into crude oil tank hatches and strangles a pregnant wife desperate to make him happy and save her family in her sleep is the very definition of THE DEVIL.
And I have serious questions about any hypothetical person who could empathize with him or would defend him.
Where is the vomiting emoji when you need it ?!