It's of course also possible that at that point in the investigation the N-8 status of the subject is confirmed but the subject is still at large. This is how actual criminal law is supposed to work. I may be wrong, but just retiring a N-8 on a bladerunner's determination of N-8 status seems less Bladerunner and more Judge Dredd.
Bear in mind that in the original Blade Runner
, Nexus-6 Replicants were
tracked down and 'retired' wherever they were found. That was Standard Operating Procedure, because a UN edict had made it illegal for Replicants to be on Earth at all.
Things have changed since then, but that's the history of the Rep-Detect Unit. This likely also contributed heavily to burnouts and suicides among Rep-Detect investigators: They were killing illegal beings who looked, acted, and even died like Humans. Very rare incidents even involved Replicants who had no idea that they weren't Human (like the second Rachel Tyrell). Blade Runners were executioners, not police, and literally anyone could be a Nexus-6. Imagine working in that kind of suspicious, paranoia-inducing environment. Small wonder Rep-Detect investigators are described as the ultimate outsiders.
How serious was the toll this took on the Blade Runners themselves? Deckard had left the RDU, and only came back when Deputy Chief Bryant made it plain that if he didn't, he'd be arrested on trumped-up charges and held until he accepted the assignment (at best). Not only that, but he was placed under arrest for no crime at all
just to get him to the office to talk to Bryant! No longer a cop, Deckard was 'little people', and thus fair game.
All that above is how it's supposed to work, and this would be how the "replicant police" would likely operate. Now do police around the world use lethal force with weak or thin justification, the so-called "horrible but lawful?" Turn on the TV. So in Bladerunner you could have a some patrol cops just blowing away a subject they think is a Nexus-8 and believed themselves justified in such an exigent retirement. The fallout from such an incident, that's a story hook.
Not only that, but the details would make the story. If the patrol cops took down a supposed Nexus-8 because he was committing a crime, that's where you start: Was this excessive force? The guy sure looks like the Nexus-8 in the file, right? The investigation seems like it's just PR, but then things start to not add up. Was an innocent 'little guy' killed because some higher-up in the LAPD had a grudge?
You can go the other way, too: Maybe the subject was taken down because he was a Nexus-8, and it sure looks like he was one, but what cause did he give? A little digging reveals that he wasn't committing any crime at the time. Did the officers know at the time that he was a Nexus-8? Is the trigger man a loose cannon with a beef against Replicants of any kind? Will the Blade Runner PCs leave it lie (after all, the officer hasn't technically committed any crime), or dish out some off-the-books justice to balance the scales? You can take this in a lot of directions and tell a completely different story each time.