There's been a whole lot of discussion on this incident across lots of forums. It's a very interesting sub-puzzle to the larger EARONS/GSK puzzle. The FBI is seemingly convinced the attacker there is GSK. I've seen all sorts of theories but I wanted to present my theory. It also likely isn't novel but I call it "my theory" because I came to it via logical induction independently. It doesn't say much but I think it answers most of the questions and makes the fewest assumptions. It doesn't offer much new insight but might prevent people from going too far down some rabbit holes.

Theory:

Brian and Katie Maggiore were walking their dog. They encountered EAR prowling around and exhibiting very suspicious behavior (possibly being weird with them directly, e.g. following from a distance and popping in and out of bushes etc.) He likely wasn't wearing his mask at this time. Brian, being a young earnest professional military man, a rank of sergeant in the Mather AFB security unit, decided to confront EAR. Brian may have attempted to question EAR or even restrict his movement, all the while getting a very good look at him. EAR made a quick calculus and thought Brian was too much of a risk to his own freedom and decided to act quickly and eliminate the threat before it possibly escalated into involving LE. Perhaps Brian's own professional countenance led EAR to believe he was LE even without Brian identifying himself as such. Katie was killed for being a direct witness.

Relevant facts:

• The attack was 9:15-10pm. This is early for an EAR attack but consistent with pre-attack prowling times reported during LE canvassing post-attacks.
• If the prowling suspect(s) reported in post-attack canvassing for other attacks was EAR it means he was commonly seen prowling often without a mask on at the time.
• Given the above, EAR never attacked anyone that noticed him prowling or acting inappropriately. If we believe the Ripon Ct. shooting was EAR, as the FBI appears to now, this was the only other time we know of that he shot to kill up to this point. And Ripon Ct. would be the only other time we know of that someone tried to apprehend him or restrict his movement up to this point as well.

What's it mean:

I think it somewhat puts to rest the notion that the Maggiores absolutely had to have known him outside of this encounter. I'm not saying they didn't but that's a pretty big assumption which I don't think we need to make and which we don't have any evidence for. This means trips down the Mather AFB drug ring/Fresno area/local acquaintance connection rabbit holes may safely be de-emphasized in anyone's hunt wrt this specific incident.

I also don't think it's likely he was attempting an EAR-style attack on the Maggiores at this time. Aside from not really fitting the location M.O., it's quite early in the evening to attempt to abduct them off the street and aside from bindings being discovered at the crime scene there's no evidence he was going to attack them specifically. The biggest strike against this though, is it seems he most likely wasn't wearing a mask when they encountered him.

Anyway, that's my thought on this incident. I think at this point eliminating noise is almost as valuable as developing new leads.