Mileage will vary based on geography and beat though.
And... I'd admit we saw some charging documents we immediately dismissed from new officers, roughly like 'this guy seemed shady and was near a crime.' We'd lay into them for that though, they'd eventually seem to figure it out.
I am not a lawyer. If anyone is in doubt I suggest speaking to a lawyer!
But if there is nothing to back it up, the guy will be realeased very soon, and if you do it repeatedly, you'll eventually get problems (and rather quickly and seriously if you lied and it can be proven).
I guess the question here is what about him makes him seem shifty to you. One would at least hope his skin color would not be factoring into that and that your judgment would have been the same for anybody else exhibiting the same behavior.
Then again, in Guantanamo Bay there are people held in custody for many years now without any charges, so these rules can be bent pretty far in the right circumstances.
Planes aren't criminals or even citizens, though. But to translate this to the 737 Max situation, when something seems to be wrong it seems entirely reasonable to ground planes in order to investigate the situation. But there should be a limit to that grounding, and a permanent ban requires some actual proof.
Of course keep arresting people for no good reason, people lose their trust in them.