Person of interest means we don't have enough to arrest; suspect means we do.
2) Someone you find attractive, you may try to go and get with, but you only have mild feelings for that person.
2) Marty: Hey, that girl over there look good, you gonna ask her out?
Daro: Nah, right now she's only a person of interest.
Also, a politically-correct term for 'Suspect'