Fun fact: John Joubert did answer this when a writer interviewed him for a book he was writing about him. His answer became the title of the book.
He killed two boys in Nebraska, not several as the article said. Here’s an informative link. http://suzukisthoughts.blogspot.com/2018/12/born-evil-story-of-john-joubert-and.html
Here’s a book written by an Omaha reporter. https://www.amazon.com/Need-Kill-True-Crime-Nebraskas-Notorious/dp/0988928310