It is interesting that after my initial evaluation of the facts it was both convenient and easy to think that it MUST be an insider that did this, or caused this tragedy. It's easy to point fingers-we do it all the time in other areas of life. But, any good sleuth tries to remove emotion and judgement when evaluating a case.
That being said, and with ALL of the work done by LE thus far, it seems reasonable that unless Jason Bourne himself pulled this off that maybe it is time to consider other possibilities. I don't like to be wishy-washy, but I may have been too quick to judge this as one thing or another. So, let's NOT overthink this. It is reasonable that Sergio may very-well have nothing to do with this, nor anyone in the entire universe of current suspects. Why? Because they haven't arrested anyone yet! There has been NO evidence of a hit, of family feuds that could rise to murder, no trysts, no drug-related activities, no bad debts, no reasonable financial motive. So think outside the box-maybe this was a fluke, or a thrill kill. We know that Liz was stalked from the early morning hours, but do we know why? If it was a hit, why the conversation before the murder? Any pro or even a hack would just blast away. There seems to be an enjoyment in the killing that could be misinterpreted as vengeance, but could simply be psychopathy.
Obviously this case is driving everyone crazy, but 4 years later and no connection has been made from the killer to the suspect pool-maybe that is because there isn't one. For all we know, it's someone who is a neighbor and had a bone to pick.
I feel that up to now everyone has tried to fit the "obvious" pieces together, and they are wondering why they don't add up. Did the killer wear a disguise to hide their identity, or are they simply a costumed killer? No one can say, 4 years later, if the killer had ANY link to the family whatsoever. They have no motive, and maybe there isn't one-or at least not the one that everyone thinks.
I'm trying to remain impartial, and like many my "gut" tells me that the killer was both known to and had it in for Liz, yet she was in many ways the MOST UNLIKELY of targets. Who would want to kill an angel? Perhaps the kindness of Liz, when compared to the dark and evil nature of the killer, is what makes this case so stark and unsettling.