When did the plural for "person" become "persons" instead of "people"? Is this just some weird Americanism, or is there a specific difference in police jargon?
It's a legal (or pseudo-legal) tic, based on a formal grammatical rule that "people" refers to a large mass (such as the "people of the United States"), and "persons" refers to a finite body of, er, people.
Technically, the plural of "person" is "persons," not "people," as the two terms share distinct Latin roots: persona vs. populus, the former referring to a physical person, and the latter to a sociocultural grouping (e.g., SPQR -- Senatus Populusque Romanus, "the Senate and People of Rome"). But we are more likely these days to use "people" as the proper plural of "person," and generally only encounter "persons" in more formal contexts.
You seem to be correct in that law enforcement uses 'persons' over 'people' more often. [1] I'm not entirely sure where the distinction comes from, but language can be such a funny thing.
Strange how I'd never noticed "missing persons" as being an odd construct before. I guess I'd just heard it so often I wasn't really aware of how the phrase was constructed.
I always took it to mean the same category of distinction made in biological categories. That is, 'people' means a simple plural person, where "persons" means a plural of person categories.
Like 'fish' means multiple fish, but 'fishes' means multiple species of fish.
Then saying 'these persons' would essentially mean 'these groups of different kinds of people.' (But that could also just be implicit regardless of your word choice.)
But... you can also use 'person' to mean the body of a person, so that 'persons' could mean multiple bodies. "They carried the weapons on their persons," for instance. Akin to how 'mice' is the plural of the animal, but 'mouses' is the plural of the computer peripheral.
