I have a question for those who are more familiar with guns and related equipment than I am.
Given all the other things this killer did to avoid detection (avoiding Nest cam, parking some distance away) or to mislead (potential disguise), WHY not use some kind of noise suppressor which might have increased the likelihood neighbors would not recognize the shootings as gun shots? Are those not possible with a revolver?
IIRC, at least 3 neighbors heard the gun shots and immediately called authorities (at least 2 of them after looking outside and seeing someone down on the ground in the Barraza's driveway).
That quick response increased the likelihood the shooter might be seen leaving the area as neighbors were able to give a description of the vehicle. The quick response also meant authorities closed off the scene early, so that evidence that might have been left by the killer was not contaminated or degraded.
One possible motivation that occurs to me is that noisy shots meant a more accurate timeline as to precisely when the shots were fired, which would be important to the determination that SB had already left the home before the shootings occurred.
Different situations.
1) situation nr 1. - I don't assume that everyone necessarily has a gun in TX. Supposedly the murderer knows how to use a gun but doesn't have one, for whatever reason (age, difficulty keeping in the house, young kids in the family, suicidal person in the family, or "just because"). Now, suddenly, the person needs a gun. One may "borrow" a revolver from a grandpa's collection, or buy one from a gun dealer's personal collection (precisely the situation that once happened in my state - depending on who you ask, the person either had no money for a better gun, or was just discharged from a mental facility, one of these cases, anyhow $50 was enough for a murder/suicide). One may simply steal a revolver, too. Even better for the purpose.
2) your idea that he wanted to provide a time frame for SB is an interesting one. Only I don't think it was that important as Sergio clocked in at work or whatever warehouse he was in. Imagine no neighbor hearing the shots. What then? Probably, Liz's body is seen an hour later when it's daytime. Sergio gets alerted later. There is still enough information on the cameras (S. leaving, cars, shots). Sergio's alibi is not the shot. Sergio's alibi is the time when he leaves the house (registered on camera, car GPS tracking, his phone GPS, his arrival at work). Personally, i think the murderers had a very limited amount of time and needed to get out as soon as possible, so alerting neighbors was not part of their plan. They might have disregarded the neighbors factor as they counted on own perfect timing (and indeed it was perfect! Really, I hope that when murderer is found - that among their personal traits, friends would mention promptness, organization, being known for responsibility, good executive functioning, picking up litter after themselves, etc, etc).
What was very important: darkness. It immensely helped them, maybe even relaxed them. If there were mistakes made, they were made at daylight. So question is, what prompted Liz to start the yard sale so early? When it is so dark around? Alone? I think the answer to this question, if known, is half the case.
Let us think of who orients well in the dark. Young people. Good nutrition (vitamin A). - Either that or being treated for acne with isotretinoin. Maybe someone who often drives at night for work, too? Deliverers, movers, truck drivers, people delivering to construction? (And why am I thinking, alpinists? Time, athleticism, runs fast, doesn't fall, nighttime is ok).
Or - drivers of schoolbuses? Could there be a different connection to the daycare center? Are some kids bused there, or is there an elementary school nearby?
Maybe they are from cosplay, of course, but I am not so sure...
