I think there's a difference from "parallel construction" and what could have happened in this case.
If they felt this guy was their suspect, there's nothing against using AI to determine that they should focus on that guy and look closer. They could instigate further, even (for example) run across someone who actually told them "yeah he said he shot a dude that day" and establish other facts and legally get a warrant.
No it's not. Parallel construction is when you hear Joe has coke in his car, and choose to follow Joe, pull him over when he speeds, and develop PC for a search from that. The grounds for the search of the car are independent.
Here the AI has primed them to falsely recognize the guy. There's no independence the way there is with parallel construction.
Your example is not parallel construction either. If you hear that Joe has coke in his car you already have probable cause to search Joe's car. You don't need to wait until he speeds, since speeding wouldn't give you a reason to search his vehicle.
Parallel construction would be: you pulled Joe over for [whatever reason] and searched his car without probable cause (maybe he seemed shifty or he was being a dick) and found coke, so you subsequently went to an informant who told you that he witnessed Joe selling coke out of his car earlier on the day of the search (which would have given you probable cause to search his car if you had talked to the informant before pulling Joe over).
The basis of parallel construction is that a real investigation would have uncovered the evidence anyway. What many people don't get is that law enforcement actually has to do the legwork of a real investigation (but knowing what to look for, and where, etc.) to show that the excluded evidence should be made admissible. It's a remedy for law enforcement to cure procedural violations of due process under the Fourth Amendment.
Yes that's one of the common situations where parallel construction is required. But it still requires the police to do the parallel investigation so that they can establish that they could have come across that evidence in an admissible manner.
I don’t think this priming theory is workable. If some witness on the street gives the police a handful of names, and they discover she didn’t actually witness the crime, are they now prohibited from investigating those people because they’re “primed”?
Facial identification is particularly difficult to do right. If you lean on people at all they will pick the closest match rather than admit they don't know. Not from dishonesty, it's just that we're not that good at recognizing strangers.
If they felt this guy was their suspect, there's nothing against using AI to determine that they should focus on that guy and look closer. They could instigate further, even (for example) run across someone who actually told them "yeah he said he shot a dude that day" and establish other facts and legally get a warrant.