This is off topic (and related to an earlier part of the thread that may no longer be of interest), but the TV series "Most Evil" is an interesting watch, with Michael Stone rating various kinds of killers on his "scale" of evil. There's also a book called "The Murder Room" (excellent true crime story) where one of the individuals featured in the book, forensic profiler Richard Walters, discusses a matrix or scale that he uses to assess an individual's propensity for violent crime. Both book and show were very useful as far as providing a blueprint for understanding the complex human nature of "evil".
With that said, I am fascinated with the Jodi Arias case and I could not fully explain why. Though it is not the defendant's evilness alone. I do think beauty and youth play a role in the interest that I have, combined with a stranger-than-fiction story and unfolding courtroom drama that is riveting and at times infuriating, or supremely gratifying once the prosecutor takes the stage. In my case, the interest may also come from being close in age with the defendant and victim.
This entire trial, with its villains, heroes (and jesters), and memorable moments: actions and statements often laced with varying degrees of stupidity, cleverness, arrogance, righteousness, and some awful playacting. I've attempted watching other trials, but they failed to hold my interest, (such as the Casey Anthony trial, beginning with prosecution's opening statement). I think the prosecutor's style in the Arias trial has really drawn me in.
Additionally, with the Arias case there are some broader themes that come into play: with the American justice system, rights of public, defendant, and victim, "trial-by-media" - to name a few. All these different things coming together can be what sets this case apart for many of us.