principal suspect
Prime suspect is the missus who hung herself.
La principale suspecte est l'épouse qui s'est pendue.
— The Wailing (2016)
Dan became the prime suspect.
Dan est devenu le principal suspect.
Benigno, do you realise you are the prime suspect?
Benigno, vous rendez-vous compte que vous êtes le principal suspect ?
— Talk to Her (2002)