I wonder a lot about that myself. It wouldn't necessarily be hard to ascertain Sergio's schedule if there was more staking out than we necessarily know about. But even so no one's a robot and the timing's too close...I need to go back and look at it, but wonder if where the perp was parked would have offered a view of Sergio's route out of the neighborhood? Otherwise the timing is very...precise.
IMO waiting even three minutes (it was 3 right?) after Sergio left is a bit too small of a window...you'd think the killer would have wanted to put at least a 10-minute buffer between him leaving and the shooting to avoid suspicion for the very reason of it looking precise, IDK that's just me. I think that was quite risky IMO.
The fact that so few people knew about the garage sale leaves two possibilities in my opinion...either the killer is someone close to Liz or, is someone who is close to a family member/friend of hers. But it seems like if the few people who knew about the garage sale divulged that info to anyone else that Liz hadn't intended to tell, LE would know about it given that they've looked through the electronic records and phones. But as I type this, I don't think using burner phones to pull off this killing is out of the realm of possibility, given the level of planning.
Here's a random question we probably won't have answered for some time...did she tell the few people who knew about the garage sale individually or was it something she may have shared in a group text? If it was the latter, it'd seem that the pool of possible suspects is even smaller.
I feel like if this killing is related to unrequited love, let's say on the part of Liz, this could have been built up in the mind of the killer/accomplice over time without her even knowing. I think about a smitten co-worker, maybe a delivery person at either one of her jobs or a customer, some kind of sub-contractor or another vendor...I think someone who got their feelings hurt could have easily turned the situation into a whole other beast if they lied to a partner or spouse and instead made it seem as though Liz was the one who was coming on to them. If the accomplice is someone who would be jealous of Liz and convinced that she needed to be eliminated to save a relationship, I could see this being motive. Just because by all accounts it *seems* as though Liz didn't have any issues with co-workers (or customers at the costume shop) doesn't mean that a co-worker and/or their partner didn't harbor any resentment toward her. Imagine if this killing was all due to some imaginary scenario made up by someone's feelings of insecurity...scary.
Following this train of thought...could a creepy neighbor or local who felt they had a connection with Liz also be responsible? I don't see why not. It's not like there had to be a major incident to piss off the wrong person if they're not capable of handling rejection. It could have been as simple as Liz being very polite but firm that being hit on or propositioned that set someone off. Some people can't handle a 'no thank you, ' and as a woman who has been relentlessly harassed before, it can be a scary world to walk around in even when you're doing your best to be civil about a situation.
<modsnip> I wonder if there is an old ex-boyfriend, or even an acquaintance who has harbored resentment toward her for quite some time, years possibly, that's been watching her since she married Sergio. Is it possible that her killer has been following her relationship and casing her neighborhood for months, maybe even years? We don't know of any alleged stalkers, but that doesn't mean someone wasn't dutifully following her every move that may have been completely unbeknownst to her. Or Sergio, perhaps Liz got in the way of an old flame that never got the chance at love with him because she got to him first.