person of interestnoun [ C ]
uk/ˌpɜː.sən əv ˈɪn.trəst//ˌpɝː.sən əv ˈɪn.trɪst/plural persons of interest USa person who the police think might have been involved in a crime, but who has not been arrested:
No one has been arrested, but several people have been labeled "persons of interest" and questioned.