It's easy for us to look at this rationally and ask wtf; we're not emotionally caught up in the internal drama battling with some moral or ethical conflict. This is deviant behavior 101. Who in their right mind would return to the scene of the crime? Yet some do. One recurring theme is the need to attract attention to oneself - like the joker's calling card. She wrote five threatening emails to herself. That's exhibiting what may be deviant narcissistic behavior, and deviant-level narcissists often think of themselves as invincible. We can only speculate based on what the media is telling us (there's a lot not being disclosed). Does this person have a mental health history or other indicators? We just don't know. All I can say is don't try putting the puzzle together here on reddit, because we lack all the pieces. It often takes skilled investigators months and years to determine the "why," and some areas of criminal psychology are left unexplained. I wrote a an essay on intelligent and successful athletes/professionals who ruined their careers breaking the law. Criminology is a very entertaining area of study. I will be following this closely.