It doesn't have anything to do with guilt, imo, but it's an entire important field of study related to killers!
It can very much help people understand the crimes better. Case in point: people don't understand how a PhD student in criminology could make such basic mistakes. To the extent that they think he didn't do it! I have a DSM entry in my head right now that could explain that, and it's a well-researched subject of its own.
I'm biased because I considered grad school for exactly this subject, lol. But it is a large part of true crime, I think it's fair to say overall, too.