Language Log has a good post on a phrase that I’ve seen cropping up increasingly in journalism:

Person of interest, called a “euphemism for a suspect” by
the National Association of Police Chiefs, is now routinely used in
investigations of all types, from murders to brush fires. 

Donna Shaw, writing in the American Journalism Review two years ago, said:

Officially, “persons of interest”
means…well, nothing. No one has ever formally defined it-not police,
not prosecutors, not journalists. The terms, “accused,” “allege,”
“arrest,” and “indict” are all dealt with in the Associated Press
Stylebook, but there is no listing for “person of interest.” Similarly,
the US Attorney’s Manual-the guide to federal criminal
prosecutions-uses the terms “suspect” “target” and “material witness,”
but “person of interest” gets no mention. So what are reporters to do?

What indeed? Journalists are stuck with using law enforcement’s word, that’s what.

So there you have it. Person of interest is an expression
that has no legal meaning, yet it carries an undefined and highly
pejorative meaning about those so designated. So far at least, it’s
apparently okay for law enforcement to use it, as long as they don’t
mind the inevitable lawsuits that will follow.