I agree with your thoughts. five years to the damn DAY was no coincidence whatsoever, none. In this psychos mind, he was justified because by looking him up on his computer , she "violated my privacy."
POS.
But if he can go off so easy and so violently, I hope the FBI and all authorities involved will track his comings and goings for the past 5 years and see if it matches with similar, unsolved murders.
I would not be surprised to learn that he didn't go 5 years without other episodes.
If He really is a sociopath, this is consistent with that type of behavior. This is what is called "upping the ante". Van der Sloot got away with it once (possibly more), so he escalates the behavior. You see this with serial killers. They intentionally leave clues, often mocking law enforcement for their predictability and ineptness. Or they do things in a ritualistic manner. Specific dates, places, etc. are important to some. When I heard the murder was five years to the day, I thought, we're getting into serial killer territory here.
CC