Were there oher Altima's in the area that night driving around?
Since there was significant delay between the crime and release it's reasonable to assume that whatever police could check was checked before and neither the car or the driver was located to this day.
Maybe they were stolen license plates IDK.
There is no way to convince LE that nothing illegal is going on if the driver would be caught with stolen licence plates. Routine checkup, and the driver would be in huge trouble. Especially at night, when there is not that many other cars driving.
But something is off here where LE asked the driver of the Altima to come forward but they haven't. Maybe they weren't local.
That seems to be pretty likely scenario. Someone from other state would have smaller chance to learn about Missy's case and that police is looking for that car's driver. For some people it could be pretty hard to recall if they were ever in Midlothian... and from the driver's perspective parking lot could look totally different so not ringing any bells even if they saw the recording sometime later.
But what that driver was doing generally isn't consider as understandable action by those looking at the recording. I don't recall any comment like "Oh yeah, this could be me, cause I sometimes do that because: ..."
Why would the Altima just drive around they obviously may have been surveiling the gun store. But if the motive was a future robbery of the gun store then I can see them not coming forward.
And doing that on rainy night while barely anything is visible yet the car and driver are extremely exposed?
Attempted robbery of gun store was the reason why this material was even discovered and given to the police. It'd be ten times easier and more convenient for a robber to check out the store during the day, pretending to be one of the customers.
Maybe the driver of the Altima was looking for a random victim at the gunstore but couldn't come across any so decided to go to the church?
Random victim in the middle of the night? Most likely not.
If LE has ruled everyone out does this mean that Missy's death was random?
No. If they ruled out every possible POI that they considered it just means that none of those people had anything to do with this crime, as far as available evidence goes. Nothing more, nothing less.
Even if they came up to the conclusion that it was almost certainly random, they still have to explore and investigate different angles if they see other scenarios as possible.
Considering how thoroughly people closest to her were investigated it's highely unlikely that any of them was involved. But Missy could be considered as locally famous. Not some Midlothian star known to everyone in the city and around it, but cause of her involvement in fitness she was known to hundred(s) time more people than average housewife would be. Lots of interactions with people, so risk of having one nutcase among them who managed to develop mortal grudge against her.
It's definitely not a likely scenario but it is a possibility.
Toxic jealousy is a thing and whoever was in this kind of relationship probably can confirm that it doesn't matter what facts are, what matters is the crazyness that goes on in jealous person's mind. Fitness/gym/pool trainers are especially good candidates as people to be jealous about and they can have no clue that something is going on, cause in reality nothing is going on.
Since all "usual" suspects were checked, investigated and ruled out IMO if Missy was not a random victim, then she was targeted by someone who managed to draw no attention to themselves during the investigation - and not cause they were criminal masterminds, but cause their motive was crazy enough to be unforeseen and with rather loose ties to her.
If not she personally was targeted, but someone among gladiators, some fitness trainer, some member of that church, some police officer or someone related to Missy (to end up incriminated as the perp) it'd be even harder to find a connection.
But - better to keep in mind that it is, excuse my language - pretty advanced rabbitholling: "possible" as far as sheer possibilities go, but as long as evidence and clues aren't pointing directly at that angle it won't lead anywhere.