Weird Events

A 27-year-old man kills his 29-year-old wife and infant daughter. He then gets on a plane to Vegas, where he rents a hotel room and proceeds to slash his wrists and ankles, killing himself.

A co-worker tells me he knew this man in high school. They were, actually, fairly close in high school.

Another co-worker suggests the wife had cheated, and that was the reason the man snapped.
It takes a weak-willed man to kill his cheating wife and infant daughter. I wonder if this co-worker is just a weak-willed.
I suggest that the man was bipolar and didn't take his medications.
It takes a mentally unstable person to believe a man kills his wife and infant daughter because of a mental instability. How mentally unstable am I?
It's revealed that days before her murder, the wife posted on Facebook that she has the most loving husband ever.
My co-worker said that he had met his high school friend's wife and daughter weeks before the incident, and they all looked perfectly happy together.

What makes something like this happen?
There won't be any answers.
Kinda like a chair leg that gets chewed on by a puppy, it can't be fixed and there's nothing you can do about it. It's gonna stay with me and gnaw at me for a while. I'll forget about it, maybe, and maybe think about it again in the future, like rubbing my hand over that chewed chair leg and being reminded of the unfixable damage.

It's kinda hanging on me like a cloud. Like smog in the top of my skull. Like an accidental spider web.