Depending on how much you believe of their story.

He said they went on a vacation and never came back. Turns out he had shot them to death, carved them up, and disposed of their remains. They found most of the parts.

Turns out the kid had been lying to his parents about a lot of things and was about to be found out.

https://en.wikipedia.org/wiki/Chandler_Halderson

A total stranger wielding a knife against you would be terrifying enough. But one's son? I know the element of surprise can overwhelm most anyone's self-defenses, but I would imagine the hesitation against taking lethal self-defense action against one's own son would have rendered them vulnerable as well.

there were moments when this crossed my mind. cant imagine a worse fate.
she did grow up to b a fine woman w whom i get along well. but there were a few tough yrs.

own/play a "violent" video game (I know nothing about video games). Mother died; father survived, but with lasting disability.

I recall being mad at my parents for one petty thing or another.. but nothing like this.

Parents want so much to believe in their children’s future — that they will one day mature into a fulfilled, content, decent life.
To know in your final hour that not only is your kid capable of killing you but that they will spend their life in prison for it must be such terrible grief.